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Venn Diagram Practice Questions

Sir Faraz Hassan

Sir Faraz Hassan

12 Jul 2026

Table of Contents
    Grade 8-9 TargetedFrom two-set foundations to the toughest three-set problems

    Venn diagrams look easy until the question stops asking you to fill one in and starts asking you to read one. These eleven questions build from a two-set diagram with an unknown in it, through shading, set notation and three-set problems, up to a quadratic Venn and a probability without replacement. Each one has a complete worked solution and mark scheme, so you can see exactly how every mark is earned.

    What are Venn diagrams?

    A Venn diagram uses overlapping circles to show how sets of things are related. Each circle is a set, the overlap is what the sets have in common, and the rectangle around them is the universal set, written as ξ, which holds everything being considered. The numbers written inside the regions usually tell you how many things are in each region, not what those things are. The notation is where most marks are lost: A ∩ B means A and B, so it is the overlap; A ∪ B means A or B, so it is everything inside either circle; and A′ means not A, so it is everything outside circle A. Brackets matter too, because (A ∪ B) ∩ C and A ∪ (B ∩ C) are different regions. At GCSE and IGCSE, Venn diagrams are used to complete a diagram from given totals, to read off probabilities including conditional probabilities, to shade a region from its set notation, and to find the highest common factor and lowest common multiple from prime factors.

    How to use this page

    1

    Try each question on paper first

    Give yourself a real attempt before looking at the solution, because that is where the learning happens.

    2

    Check the calculator icon

    A crossed-out calculator means non-calculator; a plain calculator means a calculator is allowed.

    3

    Reveal the worked solution

    Open the solution under each question and compare it with your own method, step by step.

    4

    Read the mark scheme

    See exactly where each method mark (M1) and accuracy mark (A1) is awarded, and remember that a completely correct Venn diagram is often worth several marks on its own.

    5

    Come back and redo it

    Repeat any question you got wrong a few days later to lock the method in.

    Download printable PDF

    11 questions with full worked solutions and mark schemes - free PDF

    Practice questions

    Work through each question, then open the worked solution to check your method. The questions get harder as you go, from Grade 6 up to Grade 9.

    Question 1, Grade 6, Non-calculator

    A garden centre recorded what its customers bought one Saturday morning.

    ξ\xi is the set of all customers that morning.

    SS is the set of customers who bought seeds.

    CC is the set of customers who bought compost.

    The Venn diagram shows the number of customers in each region.

    Venn diagram with universal set and two overlapping sets S and C; the regions are labelled 4x + 1, 2x + 5 and x + 3, with 16 outside both setsξSC4x + 12x + 5x + 316

    (a) Given that n(ξ)=60n(\xi) = 60, find the value of xx. [2 marks]

    (b) Find n(SC)n(S \cup C). [2 marks]

    (c) One of the customers is chosen at random. Find P(SC)P(S \cap C). Give your answer as a fraction in its simplest form. [2 marks]

    (a)x=x =
    (b)n(SC)=n(S \cup C) =
    (c)P(SC)=P(S \cap C) =
    [Total 6 marks]
    GRADE6
    Show solution & mark schemeHide solution & mark scheme

    Question 1 - Exam Solution

    Understanding the Question
    Given
    A two-set Venn diagram for a garden centre's customers, with SS the customers who bought seeds and CC the customers who bought compost.
    Regions: SS only =4x+1= 4x + 1, SC=2x+5S \cap C = 2x + 5, CC only =x+3= x + 3, and 16 outside both circles.
    n(ξ)=60n(\xi) = 60.
    Find
    (a) The value of xx.
    (b) n(SC)n(S \cup C).
    (c) P(SC)P(S \cap C), as a fraction in its simplest form.
    Plan the Solution
    • The four regions of a two-set Venn diagram account for every element, so add all four and set the total equal to n(ξ)n(\xi). That gives one equation in xx.
    • Solve it, then substitute xx back to turn every region into a number.
    • For the union, add the three regions the circles cover. For the probability, put the overlap over n(ξ)n(\xi), not over the union.
    Part (a): Find the value of xx  [2 marks]
    Rule - The four regions fill the universal set: every element of ξ\xi lies in exactly one region of a two-set Venn diagram, so the four values add up to n(ξ)n(\xi).
    Step 1: Add all four regions and set the total equal to n(ξ).
    (4x+1)+(2x+5)+(x+3)+16=60(4x + 1) + (2x + 5) + (x + 3) + 16 = 60
    (Reason: The three regions inside the circles and the 16 outside them account for every customer, so together they make the whole of ξ\xi. Forgetting the 16 is the most common error here.)
    Step 2: Collect like terms.
    7x+25=607x + 25 = 60
    (Reason: 4x+2x+x=7x4x + 2x + x = 7x, and 1+5+3+16=251 + 5 + 3 + 16 = 25.)
    Step 3: Solve for x.
    7x=357x = 35
    x=5x = 5
    (Reason: Subtract 25 from both sides, then divide both sides by 7.)
    x=5x = 5
    Mark scheme
    StepMarkDescriptionGot it?
    (4x+1)+(2x+5)+(x+3)+16=60(4x + 1) + (2x + 5) + (x + 3) + 16 = 60M1Method - all four regions add to n(ξ)
    x=5x = 5A1Accuracy - correct value of x

    Full marks: 2/2

    Part (b): Find n(SC)n(S \cup C)  [2 marks]
    Rule - Union: n(SC)n(S \cup C) counts every element in SS, in CC, or in both. On the diagram that is everything the two circles cover.
    Step 1: Substitute x = 5 into the three regions inside the circles.
    S only=4(5)+1=21S \text{ only} = 4(5) + 1 = 21
    SC=2(5)+5=15S \cap C = 2(5) + 5 = 15
    C only=5+3=8C \text{ only} = 5 + 3 = 8
    The completed Venn diagram with x = 5 substituted: 21 in S only, 15 in the overlap, 8 in C only, and 16 outside both setsξSC2115816
    (Reason: With xx known, each expression becomes a number of customers.)
    Step 2: Add the three regions inside the circles.
    n(SC)=21+15+8=44n(S \cup C) = 21 + 15 + 8 = 44
    (Reason: The union is everything inside either circle. The 16 outside is not part of the union, so it is not added.)
    n(SC)=44n(S \cup C) = 44
    Mark scheme
    StepMarkDescriptionGot it?
    Substitute x=5x = 5 to get 21, 15 and 8M1Method - evaluate the three regions
    n(SC)=44n(S \cup C) = 44A1Accuracy - correct union

    Full marks: 2/2

    Part (c): Find P(SC)P(S \cap C)  [2 marks]
    Rule - Probability: P(event)=number of favourable outcomestotal number of outcomesP(\text{event}) = \dfrac{\text{number of favourable outcomes}}{\text{total number of outcomes}}, then simplify the fraction.
    Step 1: Write down n(S ∩ C).
    n(SC)=2(5)+5=15n(S \cap C) = 2(5) + 5 = 15
    (Reason: SCS \cap C is the overlap, the customers who bought both seeds and compost.)
    Step 2: Divide by the total number of customers.
    P(SC)=1560P(S \cap C) = \dfrac{15}{60}
    (Reason: The customer is chosen at random from all of ξ\xi, so the denominator is n(ξ)=60n(\xi) = 60, not 44. Using the union by mistake is the classic trap in this part.)
    Step 3: Simplify the fraction.
    1560=14\dfrac{15}{60} = \dfrac{1}{4}
    (Reason: Divide the numerator and the denominator by 15.)
    P(SC)=14P(S \cap C) = \dfrac{1}{4}
    Mark scheme
    StepMarkDescriptionGot it?
    n(SC)=15n(S \cap C) = 15, or the fraction 1560\dfrac{15}{60}M1Method - correct numerator over n(ξ)
    P(SC)=14P(S \cap C) = \dfrac{1}{4}A1Accuracy - simplified fraction

    Full marks: 2/2

    Verification
    Check 1: The completed Venn accounts for everyone: 21+15+8+16=60=n(ξ)21 + 15 + 8 + 16 = 60 = n(\xi).
    Check 2: The union, found a different way: n(S)=21+15=36n(S) = 21 + 15 = 36 and n(C)=15+8=23n(C) = 15 + 8 = 23, so n(SC)=36+2315=44n(S \cup C) = 36 + 23 - 15 = 44. This agrees with part (b).
    Check 3: The union, found a third way: everything except the 16 outside, so 6016=4460 - 16 = 44. Three independent routes, the same answer.
    Check 4: The probability is sensible: 14\dfrac{1}{4} of 60 is 15, which is exactly n(SC)n(S \cap C).

    Question 2, Grade 6, Non-calculator

    ξ\xi is the set of integers from 1 to 30.

    Set AA is made up of the numbers generated by the sequence 5n25n - 2, where nn is a positive integer.

    Set BB is made up of the numbers generated by the sequence n2+2n^2 + 2, where nn is a positive integer.

    (a) List the elements of set AA and the elements of set BB. [2 marks]

    (b) Complete the Venn diagram to show the number of elements in each region.

    A blank Venn diagram with a universal set box and two overlapping sets A and B, ready to be completed with the number of elements in each regionξAB

    [3 marks]

    (c) Complete each statement using one of the symbols \in, \notin, \subset or ⊄\not\subset.

    (i) 18  AB18 \ \rule{22pt}{0.5pt} \ A \cap B

    (ii) {3, 6, 8}  B\{3,\ 6,\ 8\} \ \rule{22pt}{0.5pt} \ B [2 marks]

    (d) A number is chosen at random from ξ\xi. Find P(AB)P(A \cap B). [1 mark]

    (c)(i)(ii)
    (d)P(AB)=P(A \cap B) =
    [Total 8 marks]
    GRADE6
    Show solution & mark schemeHide solution & mark scheme

    Question 2 - Exam Solution

    Understanding the Question
    Given
    ξ\xi is the set of integers from 1 to 30, so n(ξ)=30n(\xi) = 30.
    Set AA is generated by 5n25n - 2 and set BB by n2+2n^2 + 2, where nn is a positive integer.
    Find
    (a) The elements of AA and of BB.
    (b) The completed Venn diagram of counts.
    (c) The correct set symbols.
    (d) P(AB)P(A \cap B).
    Plan the Solution
    • Substitute n=1,2,3,n = 1, 2, 3, \ldots into each rule and stop as soon as the value goes past 30.
    • Compare the two lists to find the elements in both. Every other element of AA goes in AA only, and every other element of BB goes in BB only.
    • The outside region is everything in ξ\xi that is in neither list, so count it by subtraction.
    Part (a): List the elements of AA and BB  [2 marks]
    Rule - Substitute and stop: put n=1,2,3,n = 1, 2, 3, \ldots into the rule and keep going until the value leaves the universal set.
    Step 1: Generate set A from 5n − 2.
    5(1)2=3,5(2)2=8,5(3)2=135(1)-2 = 3, \quad 5(2)-2 = 8, \quad 5(3)-2 = 13
    5(4)2=18,5(5)2=23,5(6)2=285(4)-2 = 18, \quad 5(5)-2 = 23, \quad 5(6)-2 = 28
    A={3, 8, 13, 18, 23, 28}A = \{3,\ 8,\ 13,\ 18,\ 23,\ 28\}
    (Reason: The next term is 5(7)2=335(7) - 2 = 33, which is bigger than 30, so it is not in ξ\xi. AA has 6 elements.)
    Step 2: Generate set B from n² + 2.
    12+2=3,22+2=6,32+2=11,42+2=18,52+2=271^2+2 = 3, \quad 2^2+2 = 6, \quad 3^2+2 = 11, \quad 4^2+2 = 18, \quad 5^2+2 = 27
    B={3, 6, 11, 18, 27}B = \{3,\ 6,\ 11,\ 18,\ 27\}
    (Reason: The next term is 62+2=386^2 + 2 = 38, which is bigger than 30. BB has 5 elements. Note that BB grows much faster than AA, because it is a quadratic rule.)
    A={3,8,13,18,23,28}B={3,6,11,18,27}A = \{3, 8, 13, 18, 23, 28\} \qquad B = \{3, 6, 11, 18, 27\}
    Mark scheme
    StepMarkDescriptionGot it?
    A={3,8,13,18,23,28}A = \{3, 8, 13, 18, 23, 28\}B1Accuracy - correct set A, stopping at 30
    B={3,6,11,18,27}B = \{3, 6, 11, 18, 27\}B1Accuracy - correct set B, stopping at 30

    Full marks: 2/2

    Part (b): Complete the Venn diagram  [3 marks]
    Rule - Overlap first: find the elements common to both lists, then everything else in AA, then everything else in BB, then subtract from n(ξ)n(\xi) to get the outside.
    Step 1: Find the elements in both lists.
    AB={3, 18}A \cap B = \{3,\ 18\}
    n(AB)=2n(A \cap B) = 2
    (Reason: 3 and 18 appear in both lists. No other value does.)
    Step 2: Find the two "only" regions.
    A only={8, 13, 23, 28}(4)A \text{ only} = \{8,\ 13,\ 23,\ 28\} \quad (4)
    B only={6, 11, 27}(3)B \text{ only} = \{6,\ 11,\ 27\} \quad (3)
    (Reason: Remove the two shared elements from each list.)
    Step 3: Find the outside region and place all four values.
    n((AB))=30(4+2+3)=309=21n((A \cup B)') = 30 - (4 + 2 + 3) = 30 - 9 = 21
    The completed Venn diagram of counts: 4 in A only, 2 in the overlap, 3 in B only, and 21 outside both sets, totalling the 30 integersξAB42321
    (Reason: 9 of the 30 integers are in at least one set, so the other 21 are in neither.)
    The completed diagram: 4 in AA only, 2 in the overlap, 3 in BB only, and 21 outside both circles.
    Mark scheme
    StepMarkDescriptionGot it?
    AB={3,18}A \cap B = \{3, 18\}, so 2 in the overlapM1Method - identifies the shared elements
    n((AB))=309=21n((A \cup B)') = 30 - 9 = 21M1Method - subtracts from n(ξ) to get the outside
    A completely correct Venn diagramA1Accuracy - all four regions correct and correctly placed

    Full marks: 3/3

    Part (c): Complete each statement  [2 marks]
    Rule - Element or subset: \in links a single element to a set. \subset links a set to a set. A dash through the symbol reverses it.
    Step 1: Part (i).
    18AB18 \in A \cap B
    (Reason: 18 is a single number, so the symbol must be \in or \notin. It appears in AA (from n=4n = 4) and in BB (from n=4n = 4), so it is in the overlap.)
    Step 2: Part (ii).
    {3, 6, 8}⊄B\{3,\ 6,\ 8\} \not\subset B
    (Reason: This is a set, so the symbol must be \subset or ⊄\not\subset. 3B3 \in B and 6B6 \in B, but 8B8 \notin B, because n2+2=8n^2 + 2 = 8 would need n2=6n^2 = 6, and 6 is not a square number. One element outside is enough to break the subset.)
    (i) 18AB(ii) {3,6,8}⊄B\text{(i) } 18 \in A \cap B \qquad \text{(ii) } \{3, 6, 8\} \not\subset B
    Mark scheme
    StepMarkDescriptionGot it?
    \inB1Accuracy - element symbol, and 18 is in both sets
    ⊄\not\subsetB1Accuracy - subset symbol negated, because 8 is not in B

    Full marks: 2/2

    Part (d): Find P(AB)P(A \cap B)  [1 mark]
    Rule - Probability: the number of favourable elements over n(ξ)n(\xi).
    Step 1: Divide and simplify.
    P(AB)=230=115P(A \cap B) = \dfrac{2}{30} = \dfrac{1}{15}
    (Reason: 2 of the 30 integers are in both sets, and the number is chosen from all of ξ\xi.)
    P(AB)=115P(A \cap B) = \dfrac{1}{15}
    Mark scheme
    StepMarkDescriptionGot it?
    230=115\dfrac{2}{30} = \dfrac{1}{15}B1Accuracy - correct probability, simplified

    Full marks: 1/1

    Verification
    Check 1: The four regions account for all 30 integers: 4+2+3+21=304 + 2 + 3 + 21 = 30.
    Check 2: The Venn rebuilds both sets: n(A)=4+2=6n(A) = 4 + 2 = 6, matching the 6 elements listed in part (a). n(B)=3+2=5n(B) = 3 + 2 = 5, matching the 5 elements listed.
    Check 3: Both lists really are complete: the next term of AA is 5(7)2=33>305(7) - 2 = 33 > 30, and the next term of BB is 62+2=38>306^2 + 2 = 38 > 30. Nothing was missed.
    Check 4: The probability works backwards: 115\dfrac{1}{15} of 30 is 2, which is exactly n(AB)n(A \cap B).

    Question 3, Grade 7, Non-calculator

    Each member of a hillwalking club was asked which of these three items they had with them.

    ξ\xi is the set of all the members.

    MM is the set of members who had a map.

    CC is the set of members who had a compass.

    WW is the set of members who had a whistle.

    (a) Describe, in words, what each of the shaded areas represents.

    (i)

    Three-set Venn diagram with the map-only region shaded: inside M but outside both C and WξMCW

    (ii)

    Three-set Venn diagram with the region outside all three sets shaded: members who had none of the three itemsξMCW

    (iii)

    Three-set Venn diagram with the central region shaded: members who had all three itemsξMCW

    [3 marks]

    (b) Write each of the three shaded regions in part (a) using set notation. [3 marks]

    (c) Shade each Venn diagram to show:

    (i) the members who had a compass only

    A blank three-set Venn diagram with three overlapping sets: M for map, C for compass and W for whistle, ready to be shadedξMCW

    (ii) all the members who had a whistle

    A blank three-set Venn diagram with three overlapping sets: M for map, C for compass and W for whistle, ready to be shadedξMCW

    (iii) the members who had exactly two of the three items

    A blank three-set Venn diagram with three overlapping sets: M for map, C for compass and W for whistle, ready to be shadedξMCW

    [3 marks]

    (b)(i)(ii)
    (iii)
    [Total 9 marks]
    GRADE7
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    Question 3 - Exam Solution

    Understanding the Question
    Given
    A three-set Venn diagram for a hillwalking club, with MM the members who had a map, CC a compass and WW a whistle.
    Find
    (a) A description in words of each shaded area.
    (b) The same three regions in set notation.
    (c) Three shaded diagrams.
    Plan the Solution
    • Read a shaded region one circle at a time: is the shading inside this circle, or outside it? Do that for all three.
    • Then translate: inside is the set, outside is the complement, and "and" between them is \cap.
    • To shade, do the reverse. Work out which regions the description covers, then shade all of them and only them.
    Part (a): Describe each shaded area  [3 marks]
    Rule - Check each circle in turn: for each of the three circles, ask whether the shading lies inside it or outside it. Three answers give the region exactly.
    Step 1: Diagram (i).
    The shading is inside M, outside C and outside W.
    (Reason: The members who had a map, but did not have a compass and did not have a whistle.)
    Step 2: Diagram (ii).
    The shading is outside M, outside C and outside W. It fills the rest of the rectangle.
    (Reason: The members who had none of the three items.)
    Step 3: Diagram (iii).
    The shading is inside M, inside C and inside W.
    (Reason: The members who had all three items: a map, a compass and a whistle.)
    (i) the members who had a map only. (ii) the members who had none of the three items. (iii) the members who had all three items.
    Mark scheme
    StepMarkDescriptionGot it?
    (i) map only, not compass and not whistleB1Accuracy - identifies all three conditions
    (ii) none of the three itemsB1Accuracy - recognises the region outside every circle
    (iii) all three itemsB1Accuracy - recognises the central region

    Full marks: 3/3

    Part (b): Write each region in set notation  [3 marks]
    Rule - Translate one symbol at a time: inside a set is the letter, outside a set is the dash, and "and" is \cap. If the shading is outside a combined region, put the dash outside a bracket.
    Step 1: Region (i).
    MCWM \cap C' \cap W'
    (Reason: Inside MM, outside CC, outside WW.)
    Step 2: Region (ii).
    (MCW)(M \cup C \cup W)'
    (Reason: Everything inside at least one circle is MCWM \cup C \cup W, so the shading is what is left. This is the one to be careful with: shade everything, then remove the union.)
    Step 3: Region (iii).
    MCWM \cap C \cap W
    (Reason: Inside all three.)
    (i) MCW(ii) (MCW)(iii) MCW\text{(i) } M \cap C' \cap W' \qquad \text{(ii) } (M \cup C \cup W)' \qquad \text{(iii) } M \cap C \cap W
    Mark scheme
    StepMarkDescriptionGot it?
    MCWM \cap C' \cap W'B1Accuracy - correct notation for "in one, out of the other two"
    (MCW)(M \cup C \cup W)'B1Accuracy - the complement of the union
    MCWM \cap C \cap WB1Accuracy - the triple intersection

    Full marks: 3/3

    Part (c): Shade each diagram  [3 marks]
    Rule - Shade every region the description covers, and nothing else: the commonest error is shading a whole circle when the word "only" appears, or shading the centre when the word "exactly" appears.
    Step 1: (i) A compass only.
    Three-set Venn diagram with the compass-only region shaded: inside C but outside both M and WξMCW
    (Reason: Inside CC, but outside both MM and WW. Only the right-hand crescent.)
    Step 2: (ii) All those who had a whistle.
    Three-set Venn diagram with the whole whistle circle shaded: all the members who had a whistle, overlaps includedξMCW
    (Reason: All of WW, so every region inside the whistle circle, overlaps included. Compare this with (i): "only" means one region, "all" means the whole circle.)
    Step 3: (iii) Exactly two of the three items.
    Three-set Venn diagram with the three pairwise-overlap regions shaded and the central region left clear: members who had exactly two of the three itemsξMCW
    (Reason: The three regions where exactly two circles overlap. The centre is not shaded: someone in the centre has three items, not two. This is the trap.)
    "Only" is a single region. "All" is the whole circle. "Exactly two" is the three pairwise overlaps with the centre left clear.
    Mark scheme
    StepMarkDescriptionGot it?
    Only the CC crescent shadedB1Accuracy - "only" means one region, not the whole circle
    The whole WW circle shadedB1Accuracy - "all" includes every overlap
    The three pairwise regions shaded, centre left clearB1Accuracy - "exactly two" excludes the centre

    Full marks: 3/3

    Verification
    Check 1: (a)(i) and (b)(i) agree: the words say "map, no compass, no whistle" and the notation says MCWM \cap C' \cap W'. Same region.
    Check 2: (a)(ii) covers the rest of the diagram: every member is in exactly one region. The union MCWM \cup C \cup W covers everything inside at least one circle, so its complement is everything else, which is exactly what is shaded.
    Check 3: (c)(i) and (c)(ii) are different regions: "a compass only" is one region, and "all those with a whistle" is four regions. If your two diagrams look the same, one of them is wrong.
    Check 4: (c)(iii) leaves the centre clear: the centre is "all three", which is three items, not two. Shading it would count those members twice over.

    Question 4, Grade 7, Non-calculator

    A cafe's menu has 50 dishes.

    ξ\xi is the set of all 50 dishes.

    VV is the set of dishes that are vegetarian.

    GG is the set of dishes that are gluten-free.

    HH is the set of dishes that are served hot.

    The Venn diagram shows the number of dishes in each region.

    Three-set Venn diagram of a cafe menu: 8 in V only, 5 in V and G only, 9 in G only, 6 in V and H only, 3 in all three, 4 in G and H only, 13 in H only, and 2 outside, totalling 50 dishesξVGH891356432

    Find:

    (a) n(V)n(V) [1 mark]

    (b) n(VG)n(V \cap G) [1 mark]

    (c) n(GH)n(G \cup H) [1 mark]

    (d) n((VG)H)n((V \cup G) \cap H) [2 marks]

    (e) n(V(GH))n(V \cup (G \cap H)) [2 marks]

    (f) Parts (d) and (e) use the same three sets and the same two symbols. Only the bracket has moved. Explain why the answers are different. [2 marks]

    (a)n(V)=n(V) =(b)n(VG)=n(V \cap G) =
    (c)n(GH)=n(G \cup H) =
    (d)n((VG)H)=n((V \cup G) \cap H) =
    (e)n(V(GH))=n(V \cup (G \cap H)) =
    [Total 9 marks]
    GRADE7
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    Question 4 - Exam Solution

    Understanding the Question
    Given
    A three-set Venn diagram of a cafe's 50 dishes, with VV vegetarian, GG gluten-free and HH served hot.
    The eight regions are 8, 5, 9, 6, 3, 4, 13 and 2.
    Find
    n(V)n(V), n(VG)n(V \cap G), n(GH)n(G \cup H), n((VG)H)n((V \cup G) \cap H) and n(V(GH))n(V \cup (G \cap H)).
    Then why the last two differ.
    Plan the Solution
    • \cap means "and", so it is the overlap. \cup means "or", so it is everything in either.
    • Always add the regions, not the set totals. A set total already contains its overlaps, so adding two of them double-counts.
    • Where there is a bracket, do the bracket first. The bracket decides which set is combined with which.
    Part (a): Find n(V)n(V)  [1 mark]
    Rule - Add the regions, not the totals: a circle is made of several regions, and every one of them counts.
    Step 1: Add the four regions inside V.
    n(V)=8+5+6+3=22n(V) = 8 + 5 + 6 + 3 = 22
    (Reason: The VV circle covers four regions: VV only, VGV \cap G only, VHV \cap H only, and all three.)
    n(V)=22n(V) = 22
    Mark scheme
    StepMarkDescriptionGot it?
    2222B1Accuracy - all four regions of V

    Full marks: 1/1

    Part (b): Find n(VG)n(V \cap G)  [1 mark]
    Rule - An overlap on a three-set Venn is TWO regions: the pairwise-only region, and the centre.
    Step 1: Add both regions of the overlap.
    n(VG)=5+3=8n(V \cap G) = 5 + 3 = 8
    (Reason: The 3 in the centre are in VV and in GG, so they count. Forgetting the centre is the commonest error here.)
    n(VG)=8n(V \cap G) = 8
    Mark scheme
    StepMarkDescriptionGot it?
    88B1Accuracy - includes the centre

    Full marks: 1/1

    Part (c): Find n(GH)n(G \cup H)  [1 mark]
    Rule - A union is everything inside either circle: or, faster, the whole diagram minus what is outside both.
    Step 1: Add every region inside G or H.
    n(GH)=9+5+3+4+13+6=40n(G \cup H) = 9 + 5 + 3 + 4 + 13 + 6 = 40
    (Reason: Quicker: everything except VV only and the outside, so 5082=4050 - 8 - 2 = 40.)
    n(GH)=40n(G \cup H) = 40
    Mark scheme
    StepMarkDescriptionGot it?
    4040B1Accuracy - correct union

    Full marks: 1/1

    Part (d): Find n((VG)H)n((V \cup G) \cap H)  [2 marks]
    Rule - Do the bracket first: VGV \cup G is everything vegetarian or gluten-free. Then H\cap H keeps only the part of that which is also hot. So every dish counted must be hot.
    Step 1: Identify the regions.
    The regions inside HH that are also inside VV or GG are: VHV \cap H only, all three, and GHG \cap H only.
    The same Venn diagram with the region (V union G) intersect H shaded: the three regions inside H that are also inside V or G, totalling 13ξVGH891356432
    (Reason: HH has four regions, but HH only (the 13 dishes that are hot and nothing else) is not in VGV \cup G, so it is excluded.)
    Step 2: Add them.
    n((VG)H)=6+3+4=13n((V \cup G) \cap H) = 6 + 3 + 4 = 13
    (Reason: Only the shaded band counts.)
    n((VG)H)=13n((V \cup G) \cap H) = 13
    Mark scheme
    StepMarkDescriptionGot it?
    Identifies the three regions 6, 3 and 4M1Method - bracket first, then intersect with H
    1313A1Accuracy

    Full marks: 2/2

    Part (e): Find n(V(GH))n(V \cup (G \cap H))  [2 marks]
    Rule - Do the bracket first: GHG \cap H is the dishes that are gluten-free and hot. Then VV \cup that keeps all of VV, plus that overlap. Nothing in VV is excluded.
    Step 1: Identify the regions.
    All four regions of VV (8, 5, 6, 3), plus GHG \cap H. But GHG \cap H is 4+34 + 3, and the 3 is already inside VV, so only the 4 is new.
    The same Venn diagram with the region V union (G intersect H) shaded: the whole of V, plus the 4 dishes that are gluten-free and hot but not vegetarian, totalling 26ξVGH891356432
    (Reason: VV contributes all 22 of its dishes, hot or not.)
    Step 2: Add them.
    n(V(GH))=22+4=26n(V \cup (G \cap H)) = 22 + 4 = 26
    (Reason: Then the 4 that are gluten-free and hot but not vegetarian are added.)
    n(V(GH))=26n(V \cup (G \cap H)) = 26
    Mark scheme
    StepMarkDescriptionGot it?
    All of VV (22), plus the 4 in GHG \cap H but not VVM1Method - bracket first, then union with V
    2626A1Accuracy

    Full marks: 2/2

    Part (f): Explain why the answers differ  [2 marks]
    Rule - The bracket decides which set is on the outside: whichever set sits outside the bracket controls the answer.
    Step 1: Look at what is outside the bracket in each.
    In (d), HH is outside the bracket, and the symbol is \cap. So every dish counted must be hot. The answer can never be bigger than n(H)n(H).
    In (e), VV is outside the bracket, and the symbol is \cup. So every dish in VV is counted, hot or not. The answer can never be smaller than n(V)n(V).
    (Reason: The two shaded regions above are completely different shapes. (d) is trapped inside HH. (e) is not, because the 16 dishes in VV that are not hot are still counted.)
    The bracket changes which set is combined last. In (d) the final operation is H\cap H, so everything must be hot, giving 13. In (e) the final operation is V\cup \, V, so all 22 vegetarian dishes are included whether they are hot or not, giving 26. Moving a bracket in set notation changes the region, exactly as moving a bracket in arithmetic changes the answer.
    Mark scheme
    StepMarkDescriptionGot it?
    States that in (d) everything must be in HH, but in (e) all of VV is includedB1Reason - identifies the set outside the bracket
    Links this to the two different shaded regions, or to 132613 \neq 26B1Reason - explains the consequence

    Full marks: 2/2

    Verification
    Check 1: Every dish is accounted for: 8+5+9+6+3+4+13+2=508 + 5 + 9 + 6 + 3 + 4 + 13 + 2 = 50.
    Check 2: Part (c) three ways: adding the six regions gives 40; 5082=4050 - 8 - 2 = 40; and inclusion-exclusion gives n(G)+n(H)n(GH)=21+267=40n(G) + n(H) - n(G \cap H) = 21 + 26 - 7 = 40. All three agree.
    Check 3: Part (d) must fit inside HH: 13n(H)=2613 \leq n(H) = 26. It does, because everything counted is hot.
    Check 4: Part (e) must contain all of VV: 26n(V)=2226 \geq n(V) = 22. It does, and the extra is exactly the 4 dishes that are gluten-free and hot but not vegetarian.

    Question 5, Grade 7, Non-calculator

    (a) Write 168 and 180 as products of their prime factors. [2 marks]

    (b) Complete the Venn diagram to show the prime factors of 168 and 180.

    A blank Venn diagram with two overlapping circles labelled 168 and 180, ready to be completed with their prime factors168180

    [2 marks]

    (c) Use the Venn diagram to write down the highest common factor (HCF) of 168 and 180. [1 mark]

    (d) Use the Venn diagram to work out the lowest common multiple (LCM) of 168 and 180. [2 marks]

    (e) Show that HCF×LCM=168×180\text{HCF} \times \text{LCM} = 168 \times 180. Explain, using the Venn diagram, why this will always be true for any two numbers. [3 marks]

    (c)HCF=\text{HCF} =(d)LCM=\text{LCM} =
    [Total 10 marks]
    GRADE7Problem solving
    Show solution & mark schemeHide solution & mark scheme

    Question 5 - Exam Solution

    Understanding the Question
    Given
    The numbers 168 and 180.
    Find
    (a) Their prime factorisations.
    (b) The completed Venn diagram.
    (c) The HCF. (d) The LCM.
    (e) That HCF×LCM=168×180\text{HCF} \times \text{LCM} = 168 \times 180, and why.
    Plan the Solution
    • Break each number down into primes and list every copy of each prime.
    • A prime goes in the middle once for each copy the two numbers share. Any copies left over stay on their own side. Getting this wrong is where the marks go.
    • The HCF is the middle. The LCM is everything.
    Part (a): Write each as a product of prime factors  [2 marks]
    Rule - Divide by the smallest prime that goes in, and keep going: stop when you reach 1.
    Step 1: Factorise 168.
    168=2×84=2×2×42=2×2×2×21=2×2×2×3×7168 = 2 \times 84 = 2 \times 2 \times 42 = 2 \times 2 \times 2 \times 21 = 2 \times 2 \times 2 \times 3 \times 7
    168=23×3×7168 = 2^3 \times 3 \times 7
    (Reason: Keep dividing by 2 while it goes in, then move on to 3.)
    Step 2: Factorise 180.
    180=2×90=2×2×45=2×2×3×15=2×2×3×3×5180 = 2 \times 90 = 2 \times 2 \times 45 = 2 \times 2 \times 3 \times 15 = 2 \times 2 \times 3 \times 3 \times 5
    180=22×32×5180 = 2^2 \times 3^2 \times 5
    (Reason: The same method. 180 has only two 2s, but two 3s.)
    168=23×3×7180=22×32×5168 = 2^3 \times 3 \times 7 \qquad 180 = 2^2 \times 3^2 \times 5
    Mark scheme
    StepMarkDescriptionGot it?
    168=23×3×7168 = 2^3 \times 3 \times 7B1Accuracy
    180=22×32×5180 = 2^2 \times 3^2 \times 5B1Accuracy

    Full marks: 2/2

    Part (b): Complete the Venn diagram  [2 marks]
    Rule - Match the copies, not the primes: a prime goes in the middle once for every copy the two numbers share. Count the copies, take the smaller count, and put that many in the middle. Whatever is left stays on its own side.
    Step 1: Match the 2s.
    168 has three 2s. 180 has two. They share two, so two 2s go in the middle, and one 2 is left over on the 168 side.
    (Reason: Writing "2" once in the middle because both numbers "have a 2" is the classic error. You must count the copies.)
    Step 2: Match the 3s.
    168 has one 3. 180 has two. They share one, so one 3 goes in the middle, and one 3 is left over on the 180 side.
    (Reason: The same rule, the other way round. Both repeated primes split.)
    Step 3: Everything else is unshared.
    The 7 belongs to 168 only. The 5 belongs to 180 only.
    The completed prime-factor Venn diagram: 2 and 7 in the 168 circle only, 2, 2 and 3 in the overlap, and 3 and 5 in the 180 circle only1681802, 72, 2, 33, 5
    (Reason: Neither number shares them, so they stay outside the middle.)
    168 only: 2 and 7. The middle: 2, 2 and 3. 180 only: 3 and 5.
    Mark scheme
    StepMarkDescriptionGot it?
    Middle =2,2,3= 2, \, 2, \, 3M1Method - matches the number of copies, not just the primes
    168 only =2,7= 2, \, 7 and 180 only =3,5= 3, \, 5A1Accuracy - all three regions correct

    Full marks: 2/2

    Part (c): Write down the HCF  [1 mark]
    Rule - The HCF is the middle: it is the biggest number that divides into both, so it is made of exactly the factors they share.
    Step 1: Multiply the middle region.
    HCF=2×2×3=12\text{HCF} = 2 \times 2 \times 3 = 12
    (Reason: Every factor in the middle divides into both numbers.)
    HCF=12\text{HCF} = 12
    Mark scheme
    StepMarkDescriptionGot it?
    1212B1Accuracy - the product of the middle region

    Full marks: 1/1

    Part (d): Work out the LCM  [2 marks]
    Rule - The LCM is everything: it is the smallest number that both divide into, so it must contain every factor of both, and it must not contain any factor twice over.
    Step 1: Multiply every factor in the diagram.
    LCM=(2×7)×(2×2×3)×(3×5)\text{LCM} = (2 \times 7) \times (2 \times 2 \times 3) \times (3 \times 5)
    LCM=14×12×15\text{LCM} = 14 \times 12 \times 15
    (Reason: The middle is used once, not twice. That is the whole point of the diagram: it stops you double-counting the shared factors.)
    Step 2: Evaluate.
    14×12=168,168×15=252014 \times 12 = 168, \qquad 168 \times 15 = 2520
    (Reason: Multiply in any order that keeps the arithmetic easy.)
    LCM=2520\text{LCM} = 2520
    Mark scheme
    StepMarkDescriptionGot it?
    Multiplies all three regions together, using the middle onceM1Method
    25202520A1Accuracy

    Full marks: 2/2

    Part (e): Show that HCF×LCM=168×180\text{HCF} \times \text{LCM} = 168 \times 180, and explain why  [3 marks]
    Rule - Read the identity off the diagram: the LCM contains the middle once. The HCF is the middle. Multiplying them therefore uses the middle twice, which is exactly once for each number.
    Step 1: Check the numbers.
    HCF×LCM=12×2520=30240\text{HCF} \times \text{LCM} = 12 \times 2520 = 30240
    168×180=30240168 \times 180 = 30240
    (Reason: The two agree, so the identity holds for this pair.)
    Step 2: Explain it from the diagram.
    Call the three regions L (168 only), M (the middle) and R (180 only). Then:
    168=L×M180=M×R168 = L \times M \qquad 180 = M \times R
    HCF=MLCM=L×M×R\text{HCF} = M \qquad \text{LCM} = L \times M \times R
    HCF×LCM=M×(L×M×R)=(L×M)×(M×R)=168×180\text{HCF} \times \text{LCM} = M \times (L \times M \times R) = (L \times M) \times (M \times R) = 168 \times 180
    (Reason: Every factor is accounted for exactly twice on each side, so the two products must be equal. Nothing about this argument depends on the numbers being 168 and 180.)
    The LCM uses the middle once, and the HCF is the middle. Multiplying them uses the middle twice, once for each number, which is exactly what 168×180168 \times 180 does. So HCF×LCM\text{HCF} \times \text{LCM} equals the product of the two numbers, for any pair.
    Mark scheme
    StepMarkDescriptionGot it?
    12×2520=30240=168×18012 \times 2520 = 30240 = 168 \times 180B1Accuracy - the calculation
    Writes 168=L×M168 = L \times M and 180=M×R180 = M \times R from the diagramM1Method - names the regions
    M×(L×M×R)=(L×M)×(M×R)M \times (L \times M \times R) = (L \times M) \times (M \times R)A1Reason - the middle is counted once for each number

    Full marks: 3/3

    Verification
    Check 1: Each circle rebuilds its own number: (2×7)×(2×2×3)=14×12=168(2 \times 7) \times (2 \times 2 \times 3) = 14 \times 12 = 168 and (3×5)×(2×2×3)=15×12=180(3 \times 5) \times (2 \times 2 \times 3) = 15 \times 12 = 180. If either fails, the Venn is wrong.
    Check 2: The HCF really is a common factor: 168÷12=14168 \div 12 = 14 and 180÷12=15180 \div 12 = 15. Both are whole numbers, and 14 and 15 share no factors, so 12 is the highest.
    Check 3: The LCM really is a common multiple: 2520÷168=152520 \div 168 = 15 and 2520÷180=142520 \div 180 = 14. Both whole. Notice that these are exactly the products of the two outer regions, swapped over.
    Check 4: The identity holds: 12×2520=30240=168×18012 \times 2520 = 30240 = 168 \times 180.

    Question 6, Grade 8, Calculator allowed

    A borough council estimates that, for a randomly chosen household in the borough:

    • the probability that the household recycles glass is 0.45
    • the probability that the household recycles food waste is 0.58
    • the probability that the household recycles both is 0.31

    (a) Find the probability that a randomly chosen household recycles neither glass nor food waste. [2 marks]

    (b) There are 2000 households in the borough. Complete the Venn diagram to show the expected number of households that recycle glass only, food waste only, both, and neither.

    A blank Venn diagram with a universal set box and two overlapping sets, G for glass and F for food waste, ready to be completedξGF

    [3 marks]

    (c) A household is chosen at random. Find the probability that it recycles glass, given that it does not recycle food waste. Give your answer as a fraction in its simplest form. [2 marks]

    (a)P(neither)=P(\text{neither}) =
    (c)P(GF)=P(G \mid F') =
    [Total 7 marks]
    GRADE8Problem solving
    Show solution & mark schemeHide solution & mark scheme

    Question 6 - Exam Solution

    Understanding the Question
    Given
    For a randomly chosen household: P(G)=0.45P(G) = 0.45, P(F)=0.58P(F) = 0.58 and P(GF)=0.31P(G \cap F) = 0.31, where GG is recycling glass and FF is recycling food waste.
    There are 2000 households in the borough.
    Find
    (a) P(neither)P(\text{neither}).
    (b) The completed Venn diagram of expected numbers.
    (c) P(GF)P(G \mid F'), as a fraction in its simplest form.
    Plan the Solution
    • For (a), use the addition rule to find P(GF)P(G \cup F), then take the complement.
    • For (b), subtract the overlap from each set total to get the "only" regions, then multiply every region probability by 2000.
    • For (c), the condition restricts the sample space to the households outside FF. That restricted total becomes the denominator.
    Part (a): Find P(neither)P(\text{neither})  [2 marks]
    Rule - The addition rule, then the complement: P(GF)=P(G)+P(F)P(GF)P(G \cup F) = P(G) + P(F) - P(G \cap F), and P(neither)=1P(GF)P(\text{neither}) = 1 - P(G \cup F).
    Step 1: Apply the addition rule.
    P(GF)=0.45+0.580.31=0.72P(G \cup F) = 0.45 + 0.58 - 0.31 = 0.72
    (Reason: Adding P(G)P(G) and P(F)P(F) counts the overlap twice, so the overlap is subtracted once.)
    Step 2: Take the complement.
    P(neither)=10.72=0.28P(\text{neither}) = 1 - 0.72 = 0.28
    (Reason: "Neither" is everything outside GFG \cup F, and all the probabilities add up to 1.)
    P(neither)=0.28P(\text{neither}) = 0.28
    Mark scheme
    StepMarkDescriptionGot it?
    P(GF)=0.45+0.580.31=0.72P(G \cup F) = 0.45 + 0.58 - 0.31 = 0.72M1Method - the addition rule, subtracting the overlap
    P(neither)=0.28P(\text{neither}) = 0.28A1Accuracy - correct probability

    Full marks: 2/2

    Part (b): Complete the Venn diagram  [3 marks]
    Rule - Subtract the overlap, then scale: each "only" region is the set total minus the overlap. The expected number in a region is its probability multiplied by the number of households.
    Step 1: Find the probability of each of the four regions.
    P(G only)=0.450.31=0.14P(G \text{ only}) = 0.45 - 0.31 = 0.14
    P(F only)=0.580.31=0.27P(F \text{ only}) = 0.58 - 0.31 = 0.27
    P(GF)=0.31P(G \cap F) = 0.31
    P(neither)=0.28 (from part (a))P(\text{neither}) = 0.28 \text{ (from part (a))}
    (Reason: P(G)P(G) counts every household that recycles glass, including those that also recycle food waste. Subtracting the overlap leaves glass only. Check: 0.14+0.31+0.27+0.28=10.14 + 0.31 + 0.27 + 0.28 = 1.)
    Step 2: Multiply each region probability by 2000.
    0.14×2000=2800.14 \times 2000 = 280
    0.31×2000=6200.31 \times 2000 = 620
    0.27×2000=5400.27 \times 2000 = 540
    0.28×2000=5600.28 \times 2000 = 560
    (Reason: The expected number in a region is its probability times the total number of households.)
    Step 3: Place the four values on the diagram.
    The completed Venn diagram: 280 in G only, 620 in the overlap, 540 in F only, and 560 outside both sets, totalling 2000 householdsξGF280620540560
    (Reason: 280 in GG only, 620 in the overlap, 540 in FF only, and 560 outside both circles.)
    The completed Venn diagram is shown above: 280 households recycle glass only, 620 recycle both, 540 recycle food waste only, and 560 recycle neither.
    Mark scheme
    StepMarkDescriptionGot it?
    P(G only)=0.14P(G \text{ only}) = 0.14 and P(F only)=0.27P(F \text{ only}) = 0.27M1Method - subtract the overlap from each set total
    Multiply each region probability by 2000M1Method - scale to expected frequencies
    A completely correct Venn diagramA1Accuracy - all four values correct and correctly placed

    Full marks: 3/3

    Part (c): Find P(GF)P(G \mid F')  [2 marks]
    Rule - A condition shrinks the sample space: "given that it does not recycle food waste" means only the households outside FF are counted. That restricted total becomes the new denominator.
    Step 1: Count the households that do not recycle food waste.
    n(F)=280+560=840n(F') = 280 + 560 = 840
    (Reason: Outside circle FF there are two regions: the 280 who recycle glass only, and the 560 who recycle neither.)
    Step 2: Of those, count the ones that recycle glass.
    n(GF)=280n(G \cap F') = 280
    (Reason: Within FF', only the "glass only" region also recycles glass.)
    Step 3: Divide.
    P(GF)=280840=13P(G \mid F') = \dfrac{280}{840} = \dfrac{1}{3}
    (Reason: The denominator is n(F)=840n(F') = 840, not 2000. This is the classic trap: once the condition is given, the sample space has shrunk.)
    P(GF)=13P(G \mid F') = \dfrac{1}{3}
    Mark scheme
    StepMarkDescriptionGot it?
    n(F)=280+560=840n(F') = 280 + 560 = 840M1Method - correct denominator (the restricted sample space)
    P(GF)=13P(G \mid F') = \dfrac{1}{3}A1Accuracy - correct simplified fraction

    Full marks: 2/2

    Verification
    Check 1: The Venn accounts for every household: 280+620+540+560=2000280 + 620 + 540 + 560 = 2000.
    Check 2: The Venn reproduces the given probabilities: n(G)=280+620=900n(G) = 280 + 620 = 900 and 9002000=0.45=P(G)\dfrac{900}{2000} = 0.45 = P(G). Likewise n(F)=620+540=1160n(F) = 620 + 540 = 1160 and 11602000=0.58=P(F)\dfrac{1160}{2000} = 0.58 = P(F).
    Check 3: Part (a) agrees with the diagram: 5602000=0.28\dfrac{560}{2000} = 0.28.
    Check 4: The conditional answer works backwards: 13\dfrac{1}{3} of 840 is 280, which is exactly n(GF)n(G \cap F').

    Question 7, Grade 8, Non-calculator

    A bookshop surveys its stock. Every book is either a hardback or a paperback.

    ξ\xi is the set of all the books in the shop.

    HH is the set of books that are hardbacks.

    FF is the set of books that are fiction.

    The Venn diagram shows the percentage of the shop's books in each region.

    Venn diagram showing the percentage of a bookshop stock in each region: 22 in H only, 24 in the overlap, 36 in F only, and 18 outside both setsξHF22243618

    (a) Find the probability that a randomly chosen book is a paperback, given that it is fiction. Give your answer as a fraction in its simplest form. [2 marks]

    (b) The shop has 800 books in total. By working out the number of fiction books and the number of paperback fiction books, show that your answer to part (a) is unchanged. [3 marks]

    (c) A customer claims that the probability a book is fiction, given that it is a paperback, must also equal the answer to part (a), because it involves the same two categories.

    Show that the customer is wrong, and find the correct probability. [3 marks]

    (a)P(HF)=P(H' \mid F) =
    (c)P(FH)=P(F \mid H') =
    [Total 8 marks]
    GRADE8Problem solving
    Show solution & mark schemeHide solution & mark scheme

    Question 7 - Exam Solution

    Understanding the Question
    Given
    A Venn diagram of a bookshop's stock, given as percentages, with HH the hardbacks (so HH' is the paperbacks) and FF the fiction.
    Regions: HH only =22= 22, HF=24H \cap F = 24, FF only =36= 36, and 18 outside both circles. These total 100.
    Find
    (a) P(HF)P(H' \mid F), as a fraction in its simplest form.
    (b) That the answer is unchanged when the shop has 800 books.
    (c) That P(FH)P(F \mid H') is not the same, and its value.
    Plan the Solution
    • The percentages already behave like counts out of 100, so they can be used directly.
    • A condition shrinks the sample space. For (a) the denominator is the fiction total, not 100.
    • For (b), scale every region by 800 and repeat. For (c), the condition changes, so the denominator changes.
    Part (a): Find P(HF)P(H' \mid F)  [2 marks]
    Rule - A condition shrinks the sample space: "given that it is fiction" means only the fiction books are counted. The fiction total becomes the denominator.
    Step 1: Find the fiction total.
    n(F)=24+36=60n(F) = 24 + 36 = 60
    (Reason: The fiction circle covers two regions: the 24 hardback fiction and the 36 paperback fiction.)
    Step 2: Of the fiction books, count the paperbacks.
    n(HF)=36n(H' \cap F) = 36
    (Reason: A paperback is a book that is not a hardback, so inside FF but outside HH. That is the FF only region.)
    Step 3: Divide and simplify.
    P(HF)=3660=35P(H' \mid F) = \dfrac{36}{60} = \dfrac{3}{5}
    (Reason: The denominator is 60, not 100. The condition has already ruled out every non-fiction book.)
    P(HF)=35P(H' \mid F) = \dfrac{3}{5}
    Mark scheme
    StepMarkDescriptionGot it?
    n(F)=24+36=60n(F) = 24 + 36 = 60M1Method - correct denominator (the restricted sample space)
    P(HF)=35P(H' \mid F) = \dfrac{3}{5}A1Accuracy - correct simplified fraction

    Full marks: 2/2

    Part (b): Show the answer is unchanged for 800 books  [3 marks]
    Rule - A percentage is a count out of 100: to convert to actual books, multiply each percentage by the total and divide by 100.
    Step 1: Convert each region to a number of books.
    22% of 800=17622\% \text{ of } 800 = 176
    24% of 800=19224\% \text{ of } 800 = 192
    36% of 800=28836\% \text{ of } 800 = 288
    18% of 800=14418\% \text{ of } 800 = 144
    The same Venn diagram with the percentages converted to actual books out of 800: 176 in H only, 192 in the overlap, 288 in F only, and 144 outside both setsξHF176192288144
    (Reason: 176+192+288+144=800176 + 192 + 288 + 144 = 800, so every book is accounted for.)
    Step 2: Find the fiction total and the paperback fiction total.
    n(F)=192+288=480n(F) = 192 + 288 = 480
    n(HF)=288n(H' \cap F) = 288
    (Reason: The same two regions as in part (a), now measured in books rather than percent.)
    Step 3: Divide.
    P(HF)=288480=35P(H' \mid F) = \dfrac{288}{480} = \dfrac{3}{5}
    (Reason: 288 and 480 are both 4.8 times the earlier 36 and 60. The scale factor appears in the numerator and the denominator, so it cancels.)
    The probability is 35\dfrac{3}{5}, exactly as in part (a). A conditional probability depends only on the ratio between two regions, so changing the size of the shop cannot change it.
    Mark scheme
    StepMarkDescriptionGot it?
    36% of 800=28836\% \text{ of } 800 = 288M1Method - convert a percentage region to a number of books
    n(F)=480n(F) = 480M1Method - correct denominator in the new scale
    288480=35\dfrac{288}{480} = \dfrac{3}{5}, unchangedA1Accuracy - shows the probability is the same

    Full marks: 3/3

    Part (c): Show the customer is wrong  [3 marks]
    Rule - Reversing a condition changes the denominator: P(AB)P(A \mid B) and P(BA)P(B \mid A) have the same numerator but different denominators, so they are generally not equal.
    Step 1: Identify what has changed.
    The condition is now "given that it is a paperback", so the denominator is the paperback total, not the fiction total.
    (Reason: The numerator, paperback fiction, is the same region. Only the sample space has moved.)
    Step 2: Find the paperback total.
    n(H)=36+18=54n(H') = 36 + 18 = 54
    (Reason: Outside the hardback circle there are two regions: the 36 paperback fiction and the 18 paperback non-fiction.)
    Step 3: Divide and compare.
    P(FH)=3654=23P(F \mid H') = \dfrac{36}{54} = \dfrac{2}{3}
    2335\dfrac{2}{3} \neq \dfrac{3}{5}
    (Reason: Same numerator (36), different denominator (54 instead of 60), so a different answer.)
    The customer is wrong. P(FH)=23P(F \mid H') = \dfrac{2}{3}, which is not equal to 35\dfrac{3}{5}. Swapping the two categories around swaps the denominator, so P(AB)P(A \mid B) and P(BA)P(B \mid A) are not the same.
    Mark scheme
    StepMarkDescriptionGot it?
    n(H)=36+18=54n(H') = 36 + 18 = 54M1Method - correct denominator for the new condition
    P(FH)=23P(F \mid H') = \dfrac{2}{3}A1Accuracy - correct simplified fraction
    States 2335\dfrac{2}{3} \neq \dfrac{3}{5}, so the customer is wrongA1Reason - the two conditionals are not equal

    Full marks: 3/3

    Verification
    Check 1: The percentages account for every book: 22+24+36+18=10022 + 24 + 36 + 18 = 100.
    Check 2: The 800 books account for every book: 176+192+288+144=800176 + 192 + 288 + 144 = 800.
    Check 3: Both scales give the same conditional: 3660=35\dfrac{36}{60} = \dfrac{3}{5} and 288480=35\dfrac{288}{480} = \dfrac{3}{5}.
    Check 4: Part (c) also survives the change of scale: n(H)=288+144=432n(H') = 288 + 144 = 432, and 288432=23\dfrac{288}{432} = \dfrac{2}{3}, matching 3654\dfrac{36}{54}.

    Question 8, Grade 8, Non-calculator

    A leisure centre has 200 members. Every member uses at least one of the swimming pool, the gym and the tennis courts.

    ξ\xi is the set of all 200 members.

    PP is the set of members who use the swimming pool.

    GG is the set of members who use the gym.

    TT is the set of members who use the tennis courts.

    92 members use the gym. Of these, 32 also use the tennis courts.

    96 members use the swimming pool. Of these, 28 also use the gym and 20 also use the tennis courts.

    12 members use all three facilities.

    (a) Complete the Venn diagram to show this information.

    A blank three-set Venn diagram with a universal set box and three overlapping sets: P for the swimming pool, G for the gym and T for the tennis courtsξPGT

    [3 marks]

    (b) Find n(PTG)n(P \cap T \cap G') and n((PGT))n((P \cup G \cup T)'). [2 marks]

    (c) One member is chosen at random. Find P(PG)P(P \cup G). [1 mark]

    (d) Given that a member uses the tennis courts, find the probability that this member also uses the swimming pool. Give your answer as a fraction in its simplest form. [2 marks]

    (b)n(PTG)=n(P \cap T \cap G') =n((PGT))=n((P \cup G \cup T)') =
    (c)P(PG)=P(P \cup G) =
    (d)P(PT)=P(P \mid T) =
    [Total 8 marks]
    GRADE8Problem solving
    Show solution & mark schemeHide solution & mark scheme

    Question 8 - Exam Solution

    Understanding the Question
    Given
    200 members, every one using at least one facility. PP is the pool, GG the gym and TT the tennis courts.
    n(G)=92n(G) = 92, of which n(GT)=32n(G \cap T) = 32. n(P)=96n(P) = 96, of which n(PG)=28n(P \cap G) = 28 and n(PT)=20n(P \cap T) = 20. n(PGT)=12n(P \cap G \cap T) = 12.
    Find
    (a) The completed Venn diagram.
    (b) n(PTG)n(P \cap T \cap G') and n((PGT))n((P \cup G \cup T)').
    (c) P(PG)P(P \cup G).
    (d) P(PT)P(P \mid T), as a fraction in its simplest form.
    Plan the Solution
    • Always fill a three-set Venn from the centre outwards. Start with the region in all three sets, then the pairwise-only regions, then the single-set regions, then whatever is left over.
    • "Of these" always means an overlap that already contains the centre, so subtract the centre from it.
    • Since every member uses at least one facility, the region outside all three circles is 0.
    Part (a): Complete the Venn diagram  [3 marks]
    Rule - Work from the centre outwards: every "of these" figure includes the members who use all three, so subtract the centre before placing a pairwise region. Then subtract everything already placed from each set total.
    Step 1: Place the centre.
    n(PGT)=12n(P \cap G \cap T) = 12
    (Reason: This is given directly, and every other overlap contains it.)
    Step 2: Place the pairwise-only regions.
    GT only=3212=20G \cap T \text{ only} = 32 - 12 = 20
    PG only=2812=16P \cap G \text{ only} = 28 - 12 = 16
    PT only=2012=8P \cap T \text{ only} = 20 - 12 = 8
    (Reason: The 32 who use the gym and tennis includes the 12 who also use the pool, so 20 use the gym and tennis but not the pool. Same for the other two.)
    Step 3: Place the single-set regions.
    P only=9616812=60P \text{ only} = 96 - 16 - 8 - 12 = 60
    G only=92201612=44G \text{ only} = 92 - 20 - 16 - 12 = 44
    (Reason: Subtract every region already inside PP from n(P)=96n(P) = 96, and likewise for GG.)
    Step 4: The last region, and the outside.
    T only=200(60+44+16+8+20+12)=40T \text{ only} = 200 - (60 + 44 + 16 + 8 + 20 + 12) = 40
    n((PGT))=0n((P \cup G \cup T)') = 0
    The completed three-set Venn diagram: 60 in P only, 44 in G only, 40 in T only, 16 in P and G only, 8 in P and T only, 20 in G and T only, 12 in all three, and 0 outsideξPGT60444016820120
    (Reason: Every member uses at least one facility, so nothing sits outside the circles, and the remaining members must be in TT only.)
    The completed diagram: 60 in PP only, 44 in GG only, 40 in TT only, 16 in PGP \cap G only, 8 in PTP \cap T only, 20 in GTG \cap T only, 12 in all three, and 0 outside.
    Mark scheme
    StepMarkDescriptionGot it?
    Centre 12, then the pairwise-only regions 20, 16 and 8M1Method - subtract the centre from each pairwise overlap
    PP only =60= 60 and GG only =44= 44M1Method - subtract the placed regions from each set total
    A completely correct Venn diagram, including TT only =40= 40A1Accuracy - all seven regions correct and correctly placed

    Full marks: 3/3

    Part (b): Find n(PTG)n(P \cap T \cap G') and n((PGT))n((P \cup G \cup T)')  [2 marks]
    Rule - Read the notation one symbol at a time: \cap means "and", \cup means "or", and a dash means "not". Translate the notation into a region, then read the number off the diagram.
    Step 1: Translate the first expression.
    n(PTG)=8n(P \cap T \cap G') = 8
    (Reason: "In PP and in TT but not in GG" is the region where only the pool and tennis circles overlap.)
    Step 2: Translate the second expression.
    n((PGT))=0n((P \cup G \cup T)') = 0
    (Reason: PGTP \cup G \cup T is everything inside at least one circle, so its complement is everything outside all three. Every member uses at least one facility, so that region is empty.)
    n(PTG)=8n((PGT))=0n(P \cap T \cap G') = 8 \qquad n((P \cup G \cup T)') = 0
    Mark scheme
    StepMarkDescriptionGot it?
    n(PTG)=8n(P \cap T \cap G') = 8B1Accuracy - correct region identified and read off
    n((PGT))=0n((P \cup G \cup T)') = 0B1Accuracy - recognises that nobody sits outside all three

    Full marks: 2/2

    Part (c): Find P(PG)P(P \cup G)  [1 mark]
    Rule - Union: PGP \cup G is everything inside the pool circle or the gym circle, or both.
    Step 1: Count the union.
    n(PG)=60+44+16+8+20+12=160n(P \cup G) = 60 + 44 + 16 + 8 + 20 + 12 = 160
    (Reason: Every region except TT only and the outside. Equivalently 200400=160200 - 40 - 0 = 160.)
    Step 2: Divide by the total.
    P(PG)=160200=45P(P \cup G) = \dfrac{160}{200} = \dfrac{4}{5}
    (Reason: The member is chosen at random from all 200.)
    P(PG)=45P(P \cup G) = \dfrac{4}{5}
    Mark scheme
    StepMarkDescriptionGot it?
    160200=45\dfrac{160}{200} = \dfrac{4}{5}B1Accuracy - correct probability, simplified

    Full marks: 1/1

    Part (d): Find P(PT)P(P \mid T)  [2 marks]
    Rule - A condition shrinks the sample space: "given that a member uses the tennis courts" restricts us to the TT circle. n(T)n(T) becomes the denominator, and it is not given: it must be read off the completed Venn.
    Step 1: Read n(T) off the diagram.
    n(T)=40+8+20+12=80n(T) = 40 + 8 + 20 + 12 = 80
    (Reason: The tennis circle covers four regions: TT only, PTP \cap T only, GTG \cap T only, and all three.)
    Step 2: Of those, count the pool users.
    n(PT)=8+12=20n(P \cap T) = 8 + 12 = 20
    (Reason: Inside TT, the pool users are the PTP \cap T only region and the all-three region.)
    Step 3: Divide and simplify.
    P(PT)=2080=14P(P \mid T) = \dfrac{20}{80} = \dfrac{1}{4}
    (Reason: The denominator is n(T)=80n(T) = 80, not 200.)
    P(PT)=14P(P \mid T) = \dfrac{1}{4}
    Mark scheme
    StepMarkDescriptionGot it?
    n(T)=40+8+20+12=80n(T) = 40 + 8 + 20 + 12 = 80M1Method - correct denominator, read off the Venn
    P(PT)=14P(P \mid T) = \dfrac{1}{4}A1Accuracy - correct simplified fraction

    Full marks: 2/2

    Verification
    Check 1: Every member is accounted for: 60+16+44+8+12+20+40+0=20060 + 16 + 44 + 8 + 12 + 20 + 40 + 0 = 200.
    Check 2: The completed Venn reproduces every given: n(P)=60+16+8+12=96n(P) = 60 + 16 + 8 + 12 = 96, n(G)=44+16+20+12=92n(G) = 44 + 16 + 20 + 12 = 92, n(PG)=16+12=28n(P \cap G) = 16 + 12 = 28, n(PT)=8+12=20n(P \cap T) = 8 + 12 = 20 and n(GT)=20+12=32n(G \cap T) = 20 + 12 = 32. Every one matches, so the diagram is right.
    Check 3: Part (c) a second way: everything except TT only, so 200400=160200 - 40 - 0 = 160, giving 45\dfrac{4}{5} again.
    Check 4: Part (d) backwards: 14\dfrac{1}{4} of n(T)=80n(T) = 80 is 20, which is exactly n(PT)n(P \cap T).

    Question 9, Grade 8, Non-calculator

    A museum recorded which galleries its visitors saw one Saturday.

    ξ\xi is the set of all the visitors that day.

    RR is the set of visitors who saw the Roman gallery.

    WW is the set of visitors who saw the wildlife gallery.

    Venn diagram of a museum’s visitors: 108 in R only, 42 in the overlap, 60 in W only, and 40 outside both sets, totalling 250ξRW108426040

    (a) Find the ratio of visitors who saw the Roman gallery to the total number of visitors. Give your answer in its simplest form. [2 marks]

    (b) A visitor is chosen at random. Find the probability that they saw the wildlife gallery, given that they saw the Roman gallery. [2 marks]

    (c) A visitor is chosen at random. Find the probability that they saw the Roman gallery, given that they saw exactly one gallery. [2 marks]

    (d) Find n(RW)n(R \cup W), and explain why this is not the number of visitors who saw exactly one gallery. [2 marks]

    (a)
    (b)P(WR)=P(W \mid R) =
    (c)
    (d)n(RW)=n(R \cup W) =
    [Total 8 marks]
    GRADE8Problem solving
    Show solution & mark schemeHide solution & mark scheme

    Question 9 - Exam Solution

    Understanding the Question
    Given
    A Venn diagram of a museum's 250 visitors, with RR the Roman gallery and WW the wildlife gallery.
    Regions: RR only =108= 108, RW=42R \cap W = 42, WW only =60= 60, and 40 saw neither.
    Find
    (a) n(R):n(ξ)n(R) : n(\xi), in its simplest form.
    (b) P(WR)P(W \mid R).
    (c) P(Rexactly one gallery)P(R \mid \text{exactly one gallery}).
    (d) n(RW)n(R \cup W), and why it differs from "exactly one".
    Plan the Solution
    • Read n(R)n(R) and n(ξ)n(\xi) off the diagram, then cancel the ratio down.
    • Every conditional restricts the sample space. For (b) the condition is a named set, so the denominator is n(R)n(R).
    • For (c) the condition is not a named set. "Exactly one" has to be built: it is the two crescent regions, and it excludes both the overlap and the outside.
    Part (a): Find the ratio  [2 marks]
    Rule - A ratio is simplified like a fraction: divide both parts by their highest common factor.
    Step 1: Read the two totals off the diagram.
    n(R)=108+42=150n(R) = 108 + 42 = 150
    n(ξ)=108+42+60+40=250n(\xi) = 108 + 42 + 60 + 40 = 250
    (Reason: The Roman circle covers two regions. The universal set covers all four.)
    Step 2: Write the ratio and cancel.
    150:250=3:5150 : 250 = 3 : 5
    (Reason: The highest common factor of 150 and 250 is 50, and 150÷50=3150 \div 50 = 3 while 250÷50=5250 \div 50 = 5.)
    n(R):n(ξ)=3:5n(R) : n(\xi) = 3 : 5
    Mark scheme
    StepMarkDescriptionGot it?
    n(R)=150n(R) = 150 and n(ξ)=250n(\xi) = 250, giving 150:250150 : 250M1Method - correct ratio before cancelling
    3:53 : 5A1Accuracy - fully simplified

    Full marks: 2/2

    Part (b): Find P(WR)P(W \mid R)  [2 marks]
    Rule - A named condition shrinks the sample space to that set: "given that they saw the Roman gallery" means the denominator is n(R)n(R).
    Step 1: Identify the denominator.
    n(R)=150n(R) = 150
    (Reason: Only the Roman visitors are counted now, not all 250.)
    Step 2: Of those, count the ones who also saw the wildlife gallery, then divide.
    P(WR)=n(RW)n(R)=42150=725P(W \mid R) = \dfrac{n(R \cap W)}{n(R)} = \dfrac{42}{150} = \dfrac{7}{25}
    (Reason: Inside the Roman circle, the wildlife visitors are the 42 in the overlap. Cancel by 6.)
    P(WR)=725P(W \mid R) = \dfrac{7}{25}
    Mark scheme
    StepMarkDescriptionGot it?
    42150\dfrac{42}{150}M1Method - correct numerator over the correct denominator
    725\dfrac{7}{25}A1Accuracy - simplified fraction

    Full marks: 2/2

    Part (c): Find P(R given exactly one gallery)  [2 marks]
    Rule - When the condition is not a named set, build it: "saw exactly one gallery" is not RR, and it is not RWR \cup W. It is the two crescent regions only. The 42 who saw both are excluded, and so are the 40 who saw neither.
    Step 1: Build the conditioning event.
    exactly one=108+60=168\text{exactly one} = 108 + 60 = 168
    The same Venn diagram with the two "exactly one gallery" regions, 108 and 60, shown in navy, and the excluded regions, the 42 who saw both and the 40 who saw neither, faded to greyξRW108604240
    (Reason: The two faded regions are excluded. Someone who saw both galleries did not see exactly one, and someone who saw neither did not see exactly one either.)
    Step 2: Of those, count the Roman visitors.
    n(R only)=108n(R \text{ only}) = 108
    (Reason: Within "exactly one", the visitors who saw the Roman gallery are precisely the 108 in the RR-only crescent.)
    Step 3: Divide and simplify.
    P(Rexactly one)=108168=914P(R \mid \text{exactly one}) = \dfrac{108}{168} = \dfrac{9}{14}
    (Reason: Cancel by 12. The denominator is 168, not 250 and not 210.)
    P(Rexactly one)=914P(R \mid \text{exactly one}) = \dfrac{9}{14}
    Mark scheme
    StepMarkDescriptionGot it?
    Denominator =108+60=168= 108 + 60 = 168M1Method - builds "exactly one" and excludes both the overlap and the outside
    914\dfrac{9}{14}A1Accuracy - simplified fraction

    Full marks: 2/2

    Part (d): Find n(RW)n(R \cup W) and explain  [2 marks]
    Rule - "At least one" is not "exactly one": the union counts everyone inside either circle, including the overlap. "Exactly one" leaves the overlap out.
    Step 1: Find the union.
    n(RW)=108+42+60=210n(R \cup W) = 108 + 42 + 60 = 210
    (Reason: Everything inside either circle. Equivalently 25040=210250 - 40 = 210, since only the 40 outside are excluded.)
    Step 2: Compare it with "exactly one".
    210168=42=n(RW)210 - 168 = 42 = n(R \cap W)
    (Reason: The difference is exactly the overlap.)
    n(RW)=210n(R \cup W) = 210. This is "at least one gallery", so it includes the 42 visitors who saw both. "Exactly one gallery" is 168, because those 42 are left out. The two differ by precisely n(RW)=42n(R \cap W) = 42.
    Mark scheme
    StepMarkDescriptionGot it?
    n(RW)=210n(R \cup W) = 210B1Accuracy - correct union
    Explains that the union includes the 42 who saw both, while "exactly one" excludes themB1Reason - the distinction between at least one and exactly one

    Full marks: 2/2

    Verification
    Check 1: Every visitor is accounted for: 108+42+60+40=250108 + 42 + 60 + 40 = 250.
    Check 2: The ratio backwards: 35\dfrac{3}{5} of 250 is 150, which is exactly n(R)n(R).
    Check 3: Part (b) backwards: 725\dfrac{7}{25} of n(R)=150n(R) = 150 is 42, which is exactly n(RW)n(R \cap W).
    Check 4: Part (c) backwards: 914\dfrac{9}{14} of 168 is 108, which is exactly the RR only region.

    Question 10, Grade 8, Non-calculator

    A community allotment has 120 plot holders. Every plot holder grows at least one of potatoes, tomatoes and beans.

    ξ\xi is the set of all 120 plot holders.

    PP is the set of plot holders who grow potatoes.

    TT is the set of plot holders who grow tomatoes.

    BB is the set of plot holders who grow beans.

    Three fifths of the plot holders grow exactly one crop.

    5% of the plot holders grow all three crops.

    20 plot holders grow potatoes and tomatoes.

    22 plot holders grow tomatoes and beans.

    62 plot holders grow potatoes.

    58 plot holders grow beans.

    (a) Complete the Venn diagram to show this information.

    A blank three-set Venn diagram with a universal set box and three overlapping sets: P for potatoes, T for tomatoes and B for beansξPTB

    [5 marks]

    (b) Find the number of plot holders who grow tomatoes. [1 mark]

    (c) A plot holder is chosen at random. Find the probability that they grow potatoes, given that they grow at least two crops. Give your answer as a fraction in its simplest form. [2 marks]

    (b)n(T)=n(T) =
    (c)
    [Total 8 marks]
    GRADE8Problem solving
    Show solution & mark schemeHide solution & mark scheme

    Question 10 - Exam Solution

    Understanding the Question
    Given
    120 plot holders, all growing at least one crop. PP is potatoes, TT is tomatoes and BB is beans.
    Three fifths grow exactly one crop. 5% grow all three. n(PT)=20n(P \cap T) = 20, n(TB)=22n(T \cap B) = 22, n(P)=62n(P) = 62 and n(B)=58n(B) = 58.
    Find
    (a) The completed Venn diagram.
    (b) n(T)n(T).
    (c) P(Pat least two crops)P(P \mid \text{at least two crops}).
    Plan the Solution
    • Start at the centre, then use each "and" figure to fill a pairwise region.
    • One region cannot be reached that way. The clue "three fifths grow exactly one crop" is the way in: if 72 grow exactly one, the other 48 grow at least two, and those 48 are precisely the four overlap regions.
    • Then use n(P)n(P) and n(B)n(B) for two of the singles, and subtract from 120 for the last.
    Part (a): Complete the Venn diagram  [5 marks]
    Rule - Turn every clue into a region: a percentage of the total gives the centre; each "and" figure gives a pairwise region once the centre is removed; and a statement about how many crops someone grows gives a whole band of the diagram.
    Step 1: The centre.
    n(PTB)=5% of 120=6n(P \cap T \cap B) = 5\% \text{ of } 120 = 6
    (Reason: This is the one figure given as a percentage of the whole allotment.)
    Step 2: Two pairwise regions.
    PT only=206=14P \cap T \text{ only} = 20 - 6 = 14
    TB only=226=16T \cap B \text{ only} = 22 - 6 = 16
    (Reason: The 20 who grow potatoes and tomatoes includes the 6 who also grow beans.)
    Step 3: The key insight, and the third pairwise region.
    exactly one crop=35×120=72\text{exactly one crop} = \dfrac{3}{5} \times 120 = 72
    at least two crops=12072=48\text{at least two crops} = 120 - 72 = 48
    PB only=48(14+16+6)=4836=12P \cap B \text{ only} = 48 - (14 + 16 + 6) = 48 - 36 = 12
    (Reason: Everyone grows at least one crop, so anyone not growing exactly one grows two or three. "At least two" is exactly the four overlap regions added together. Three of them are known, so the fourth falls out.)
    Step 4: The single-crop regions.
    P only=62(14+12+6)=30P \text{ only} = 62 - (14 + 12 + 6) = 30
    B only=58(12+16+6)=24B \text{ only} = 58 - (12 + 16 + 6) = 24
    T only=120(30+14+12+6+16+24)=120102=18T \text{ only} = 120 - (30 + 14 + 12 + 6 + 16 + 24) = 120 - 102 = 18
    The completed three-set Venn diagram: 30 in P only, 18 in T only, 24 in B only, 14 in P and T only, 12 in P and B only, 16 in T and B only, 6 in all three, and 0 outsideξPTB30182414121660
    (Reason: Subtract every region already inside PP from n(P)=62n(P) = 62, and likewise for BB. The last region is whatever is left of the 120.)
    The completed diagram: 30 in PP only, 18 in TT only, 24 in BB only, 14 in PTP \cap T only, 12 in PBP \cap B only, 16 in TBT \cap B only, 6 in all three, and 0 outside.
    Mark scheme
    StepMarkDescriptionGot it?
    n(PTB)=6n(P \cap T \cap B) = 6M1Method - a percentage of the total gives the centre
    PTP \cap T only =14= 14 and TBT \cap B only =16= 16M1Method - subtract the centre from each pairwise overlap
    "at least two" =12072=48= 120 - 72 = 48, so PBP \cap B only =12= 12M1Method - uses the "exactly one" clue to reach the fourth overlap
    PP only =30= 30 and BB only =24= 24M1Method - subtract the placed regions from each set total
    A completely correct Venn diagram, including TT only =18= 18A1Accuracy - all seven regions correct and correctly placed

    Full marks: 5/5

    Part (b): Find n(T)n(T)  [1 mark]
    Rule - The completed diagram knows more than the question told you: n(T)n(T) was never given, but every region inside TT now has a number.
    Step 1: Add the four regions inside the tomato circle.
    n(T)=18+14+16+6=54n(T) = 18 + 14 + 16 + 6 = 54
    (Reason: The tomato circle covers TT only, PTP \cap T only, TBT \cap B only, and all three.)
    n(T)=54n(T) = 54
    Mark scheme
    StepMarkDescriptionGot it?
    n(T)=18+14+16+6=54n(T) = 18 + 14 + 16 + 6 = 54B1Accuracy - correct total read off the completed Venn

    Full marks: 1/1

    Part (c): Find P(P given at least two crops)  [2 marks]
    Rule - "At least two" is a band, not a set: on a three-set Venn it is every region where two or three circles overlap. That is four regions, not one.
    Step 1: Build the denominator.
    at least two=14+12+16+6=48\text{at least two} = 14 + 12 + 16 + 6 = 48
    The same Venn diagram with the four "at least two crops" regions, 14, 12, 16 and 6, shown in navy, and the three single-crop regions and the empty outside faded to slateξPTB14121663018240
    (Reason: The three faded single-crop regions are excluded, and so is the outside. The denominator is 48, not 120.)
    Step 2: Of those 48, count the ones who grow potatoes.
    14+12+6=3214 + 12 + 6 = 32
    (Reason: Inside the potato circle, the "at least two" regions are PTP \cap T only, PBP \cap B only and all three. The 16 who grow tomatoes and beans grow at least two crops but not potatoes, so they are in the denominator and not the numerator.)
    Step 3: Divide and simplify.
    P(Pat least two)=3248=23P(P \mid \text{at least two}) = \dfrac{32}{48} = \dfrac{2}{3}
    (Reason: Cancel by 16.)
    P(Pat least two)=23P(P \mid \text{at least two}) = \dfrac{2}{3}
    Mark scheme
    StepMarkDescriptionGot it?
    Denominator =14+12+16+6=48= 14 + 12 + 16 + 6 = 48, numerator =14+12+6=32= 14 + 12 + 6 = 32M1Method - correct four-region denominator and three-region numerator
    23\dfrac{2}{3}A1Accuracy - simplified fraction

    Full marks: 2/2

    Verification
    Check 1: Every plot holder is accounted for: 30+18+24+14+12+16+6+0=12030 + 18 + 24 + 14 + 12 + 16 + 6 + 0 = 120.
    Check 2: The clue that built the diagram is reproduced by it: the three single-crop regions total 30+18+24=7230 + 18 + 24 = 72, which is exactly 35\dfrac{3}{5} of 120. The clue was used to derive the diagram, and the finished diagram gives it straight back.
    Check 3: The completed Venn reproduces every other given: n(P)=30+14+12+6=62n(P) = 30 + 14 + 12 + 6 = 62, n(B)=24+12+16+6=58n(B) = 24 + 12 + 16 + 6 = 58, n(PT)=14+6=20n(P \cap T) = 14 + 6 = 20 and n(TB)=16+6=22n(T \cap B) = 16 + 6 = 22. Every one matches.
    Check 4: Part (c) backwards: 23\dfrac{2}{3} of 48 is 32, which is exactly the number who grow potatoes and at least two crops.

    Question 11, Grade 9, Calculator allowed

    A school orchestra has 55 members.

    ξ\xi is the set of all 55 members.

    VV is the set of members who play the violin.

    CC is the set of members who play the cello.

    Venn diagram with universal set and two overlapping sets V and C; the regions are labelled n(n + 5), n, 3n minus 2, and 9 minus n outside both setsξVCn(n + 5)n3n − 29 − n

    (a) Show that n2+8n48=0n^2 + 8n - 48 = 0. [3 marks]

    (b) Solve the equation to find the value of nn, and write down the number of members in each region of the Venn diagram. [3 marks]

    (c) Two different members of the orchestra are chosen at random. Find the probability that they both play the violin. [3 marks]

    (b)n=n =
    (c)P(both play the violin)=P(\text{both play the violin}) =
    [Total 9 marks]
    GRADE9Problem solving
    Show solution & mark schemeHide solution & mark scheme

    Question 11 - Exam Solution

    Understanding the Question
    Given
    A Venn diagram for the 55 members of a school orchestra, with VV the violinists and CC the cellists.
    Regions: VV only =n(n+5)= n(n + 5), VC=nV \cap C = n, CC only =3n2= 3n - 2, and 9n9 - n outside both circles.
    Find
    (a) That n2+8n48=0n^2 + 8n - 48 = 0.
    (b) The value of nn, and every region.
    (c) The probability that two different members both play the violin.
    Plan the Solution
    • The four regions fill the universal set, so add them and set the total equal to 55. Because one region is a product, this gives a quadratic, not a linear equation.
    • A quadratic has two roots. Only one can be a number of people, so test both against the diagram.
    • The two members are different, so the second is chosen from what is left. This is without replacement.
    Part (a): Show that n2+8n48=0n^2 + 8n - 48 = 0  [3 marks]
    Rule - The four regions fill the universal set: every member lies in exactly one region, so the four expressions add up to n(ξ)=55n(\xi) = 55.
    Step 1: Add all four regions and set the total equal to 55.
    n(n+5)+n+(3n2)+(9n)=55n(n + 5) + n + (3n - 2) + (9 - n) = 55
    (Reason: The three regions inside the circles and the region outside them account for every member.)
    Step 2: Expand the bracket and collect like terms.
    n2+5n+n+3n2+9n=55n^2 + 5n + n + 3n - 2 + 9 - n = 55
    n2+8n+7=55n^2 + 8n + 7 = 55
    (Reason: n(n+5)=n2+5nn(n + 5) = n^2 + 5n. Then 5n+n+3nn=8n5n + n + 3n - n = 8n, and 2+9=7-2 + 9 = 7.)
    Step 3: Rearrange so the quadratic equals zero.
    n2+8n48=0n^2 + 8n - 48 = 0
    (Reason: Subtract 55 from both sides, and 755=487 - 55 = -48.)
    Therefore n2+8n48=0n^2 + 8n - 48 = 0, as required.
    Mark scheme
    StepMarkDescriptionGot it?
    n(n+5)+n+(3n2)+(9n)=55n(n + 5) + n + (3n - 2) + (9 - n) = 55M1Method - all four regions add to n(ξ)
    n2+8n+7=55n^2 + 8n + 7 = 55M1Method - expands and collects correctly
    n2+8n48=0n^2 + 8n - 48 = 0A1Accuracy - reaches the required form

    Full marks: 3/3

    Part (b): Solve, and complete the Venn diagram  [3 marks]
    Rule - A quadratic has two roots, but a region cannot: solve, then reject any root that would put a negative number of people in a region.
    Step 1: Factorise.
    n2+8n48=0n^2 + 8n - 48 = 0
    (n+12)(n4)=0(n + 12)(n - 4) = 0
    (Reason: 12×(4)=4812 \times (-4) = -48 and 12+(4)=812 + (-4) = 8.)
    Step 2: Test both roots against the diagram.
    n=12orn=4n = -12 \quad \text{or} \quad n = 4
    If n=12n = -12, the overlap would hold 12-12 members and the cello-only region 38-38. A region cannot hold a negative number of people, so n=12n = -12 is rejected.
    n=4n = 4
    (Reason: It is not enough to say "nn must be positive". The reason it must be positive is that every region counts people.)
    Step 3: Substitute n = 4 into each region.
    V only=4(4+5)=36V \text{ only} = 4(4 + 5) = 36
    VC=4V \cap C = 4
    C only=3(4)2=10C \text{ only} = 3(4) - 2 = 10
    neither=94=5\text{neither} = 9 - 4 = 5
    The completed Venn diagram with n = 4 substituted: 36 in V only, 4 in the overlap, 10 in C only, and 5 outside both sets, totalling 55ξVC364105
    (Reason: 36+4+10+5=5536 + 4 + 10 + 5 = 55, so every member is accounted for.)
    n=4n = 4, and the completed Venn diagram is 36, 4, 10 and 5.
    Mark scheme
    StepMarkDescriptionGot it?
    (n+12)(n4)=0(n + 12)(n - 4) = 0M1Method - correct factorisation
    n=4n = 4, rejecting n=12n = -12 with a reasonA1Accuracy - correct root, correctly justified
    Regions 36, 4, 10 and 5A1Accuracy - all four regions correct

    Full marks: 3/3

    Part (c): Find P(both play the violin)  [3 marks]
    Rule - "Two different members" means WITHOUT replacement: the first member is not put back, so the second is chosen from one fewer person, and one fewer violinist.
    Step 1: Find how many members play the violin.
    n(V)=36+4=40n(V) = 36 + 4 = 40
    (Reason: The violin circle covers VV only and the overlap.)
    Step 2: Write both probabilities.
    P(1st plays violin)=4055P(\text{1st plays violin}) = \dfrac{40}{55}
    P(2nd plays violin)=3954P(\text{2nd plays violin}) = \dfrac{39}{54}
    (Reason: After a violinist is chosen, 39 violinists remain out of 54 members. Both the top and the bottom go down by one. This is the whole point of "two different members".)
    Step 3: Multiply and simplify.
    P(both)=4055×3954=811×1318=5299P(\text{both}) = \dfrac{40}{55} \times \dfrac{39}{54} = \dfrac{8}{11} \times \dfrac{13}{18} = \dfrac{52}{99}
    (Reason: Cancel each fraction first, then multiply.)
    P(both play the violin)=5299P(\text{both play the violin}) = \dfrac{52}{99}
    Mark scheme
    StepMarkDescriptionGot it?
    n(V)=40n(V) = 40M1Method - correct number of violinists
    4055×3954\dfrac{40}{55} \times \dfrac{39}{54}M1Method - without replacement, both numerator and denominator reduced by one
    5299\dfrac{52}{99}A1Accuracy - correct simplified fraction

    Full marks: 3/3

    Verification
    Check 1: Substitute n=4n = 4 back into the original expressions: 4(4+5)+4+(3(4)2)+(94)=36+4+10+5=554(4+5) + 4 + (3(4) - 2) + (9 - 4) = 36 + 4 + 10 + 5 = 55, which is n(ξ)n(\xi).
    Check 2: The rejected root really is impossible: at n=12n = -12 the overlap would be 12-12 and the cello-only region 3(12)2=383(-12) - 2 = -38. Neither can be a number of people.
    Check 3: Counting check: 40 members play the violin, so 15 do not. The two regions outside the violin circle are 10 and 5, and 10+5=1510 + 5 = 15.
    Check 4: The probability is sensible: 5299=0.5253\dfrac{52}{99} = 0.5253, just below (4055)2=0.5289\left(\dfrac{40}{55}\right)^2 = 0.5289. Without replacement must give a slightly smaller answer than with replacement, and it does.
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    Frequently Asked Questions

    A Venn diagram uses overlapping circles to show how sets of things are related. Each circle is a set, the overlap is what the sets have in common, and the rectangle around them is the universal set, which holds everything being considered. The numbers inside the regions usually tell you how many items are in each region, not what those items are. Venn diagrams appear on both GCSE and IGCSE papers, most often in probability questions.

    The intersection symbol ∩ means "and", so A ∩ B is the overlap of the two circles. The union symbol ∪ means "or", so A ∪ B is everything inside either circle, including the overlap. A prime after a set, written A′, means the complement, or "not", so A′ is everything outside circle A. Brackets matter: (A ∪ B) ∩ C is not the same region as A ∪ (B ∩ C), and the two usually give different answers.

    Always work from the centre outwards. Start with the number in all three sets, because every other overlap contains it. Then fill each pairwise overlap by subtracting the centre from the "and" figure you are given. Then fill each single-set region by subtracting everything already placed from that set's total. Whatever is left over goes in the last region, or outside the circles.

    A condition shrinks the sample space. "Given that" tells you which region to use as the denominator, and it is almost never the whole universal set. The probability of A given B is the number in A ∩ B divided by the number in B, not by the total. If the condition is not a named set, such as "given that they chose exactly one", you have to build that region from the diagram yourself before you can use it.

    Write each number as a product of its prime factors, then put the shared factors in the overlap and the rest in the outer regions. Count the copies: if one number has three 2s and the other has two, then two 2s go in the middle and one stays outside. The HCF is the product of the overlap, and the LCM is the product of everything in the diagram.

    Venn diagrams appear on both tiers. Foundation questions usually ask you to complete a diagram and read a simple probability from it. Higher questions go further: conditional probability, three-set problems, algebraic regions and probability without replacement. This page is aimed at the Higher tier work, from Grade 6 up to Grade 9.

    Keep revising

    Once you are confident with Venn diagrams, browse the full topic lists for GCSE Maths topics and IGCSE Maths topics, and check the GCSE grade boundaries and IGCSE grade boundaries to set your target. For more exam-style practice, try the Circle Theorems Practice Questions and the Simultaneous Equations Practice Questions.

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