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Edexcel IGCSE 4MA1/2H, Wednesday 4 June 2025: Worked Solutions, Questions 11 to 19

Sir Faraz Hassan

Sir Faraz Hassan

31 Aug 2026

Table of Contents
    Edexcel International GCSE Mathematics A (4MA1)4MA1/2H - Higher Tier - Wednesday 4 June 2025100 marks  ·  2 hours  ·  Calculator allowed
    Back to questions 1 to 10

    This is part two of three. Questions 1 to 10, the paper's overview and the frequently asked questions are on the first page.

    Original worked solutions for Edexcel International GCSE Mathematics A, Paper 4MA1/2H (Higher Tier), June 2025 series, sat Wednesday 4 June 2025 –100 marks, 2 hours, calculator allowed. The questions have been reworded; all numerical values match the original paper. The official question paper and mark scheme are published by Pearson Edexcel. This resource reproduces neither the exam paper nor the official mark scheme.
    Both are PDF files hosted by Pearson: official question paper (PDF) and official mark scheme (PDF).

    Try each question yourself first, then open the worked solution to check your method and see exactly where each method mark (M1) and accuracy mark (A1) is earned. The questions follow the same order as the original paper and carry the same marks.

    Download printable PDF

    All 26 questions with a full worked solution and mark scheme - free PDF

    Worked solutions, questions 11 to 19 of 26

    Question 11, Calculator allowed

    Yusuf has a jar of glass beads.

    1717 of the beads are green
    2828 of the beads are yellow
    the rest of the beads are purple

    Yusuf is going to take at random a bead from the jar.

    The probability that Yusuf will take a purple bead is 49\dfrac{4}{9}

    Work out the number of purple beads that are in the jar. [3 marks]

    [Total 3 marks]
    Show solution & mark schemeHide solution & mark scheme

    Question 11 - Exam Solution

    Understanding the Question
    Given
    The jar holds 1717 green beads, 2828 yellow beads, and some purple beads.
    One bead is taken at random, and the probability that it is purple is 49\dfrac{4}{9}.
    Find
    The number of purple beads in the jar. The total is unknown as well, so expect to find the whole jar on the way to the 44 ninths that are purple.
    Plan the Solution
    • The green and the yellow beads are exactly the beads that are not purple, so add them: that is the only part of the jar the question actually counts.
    • Purple and not purple are the only two outcomes, so their probabilities add to 11. That turns the counted beads into a known fraction of the jar.
    • Split that fraction into its 55 equal ninths to find one ninth, then build the whole jar back up and take the purple share.
    Worked Solution [3 marks]
    Rule - the probability of taking a purple bead is the number of purple beads over the total number of beads, and the probabilities of all the outcomes add to 11.
    Step 1: count the beads that are not purple
    17+28=4517 + 28 = 45
    (Reason: Every bead is green, yellow or purple, so the 1717 green and the 2828 yellow beads together are all the beads that are not purple.)
    Step 2: find the probability of not purple
    149=591 - \dfrac{4}{9} = \dfrac{5}{9}
    (Reason: Purple and not purple are the only two outcomes, so their probabilities add to 11. Those 4545 beads therefore make up 59\dfrac{5}{9} of the jar.)
    Step 3: work out one ninth of the jar
    455=9\dfrac{45}{5} = 9
    (Reason: Those 4545 beads are 55 of the 99 equal ninths, so one ninth is 4545 shared into 55 equal groups.)
    Step 4: build the whole jar, then take the purple share
    9×9=819 \times 9 = 81
    4×9=364 \times 9 = 36
    (Reason: The whole jar is 99 ninths, so it holds 8181 beads, and the purple beads are the 44 ninths that are left once the counted beads are taken out.)
    3636 purple beads
    Verification
    Check 1: Put the answer back in. The jar would then hold 1717 green, 2828 yellow and 3636 purple beads, so work out the probability of purple from those counts. 3617+28+36=3681=49\dfrac{36}{17 + 28 + 36} = \dfrac{36}{81} = \dfrac{4}{9}
    Check 2: Cross-multiply instead of dividing: nine lots of the purple beads should equal four lots of all the beads. 9×36=3249 \times 36 = 324 and 4×81=3244 \times 81 = 324
    Check 3: A different quantity altogether. The beads that are not purple should outnumber the purple ones in the ratio five to four, because their probabilities are five ninths and four ninths. 4536=54\dfrac{45}{36} = \dfrac{5}{4}
    Mark Scheme Breakdown
    StepMarkDescriptionGot it?
    17+2894\dfrac{17 + 28}{9 - 4} or 455\dfrac{45}{5} or 149(=59)1 - \dfrac{4}{9} \left( = \dfrac{5}{9} \right) or (17+28=)59(17 + 28 =) \dfrac{5}{9} oe or pp+28+17=49\dfrac{p}{p + 28 + 17} = \dfrac{4}{9} oe or pp+45=49\dfrac{p}{p + 45} = \dfrac{4}{9} or m45m=49\dfrac{m - 45}{m} = \dfrac{4}{9}M1Allow 0.55(555)0.55(555\ldots) or 55(.555)%55(.555\ldots)\% truncated or rounded
    17+285×4\dfrac{17 + 28}{5} \times 4 or 455×4\dfrac{45}{5} \times 4 or 17+28their 59(=81)\dfrac{17 + 28}{\text{their } \dfrac{5}{9}} (= 81) or 45their 59(=81)\dfrac{45}{\text{their } \dfrac{5}{9}} (= 81) or (17+28)×their 95(=81)(17 + 28) \times \text{their } \dfrac{9}{5} (= 81) or 45×their 95(=81)45 \times \text{their } \dfrac{9}{5} (= 81) or their 59=17+28n\text{their } \dfrac{5}{9} = \dfrac{17 + 28}{n} oe or n=81n = 81 or 9p=4(p+28+17)9p = 4(p + 28 + 17) or 9p4p=1809p - 4p = 180 oe or 5p=1805p = 180 oe or 9(m45)=4m9(m - 45) = 4m or 9m4m=4059m - 4m = 405 oe or 5m=4055m = 405 oe or m=81m = 81M1for the correct calculation for the total number of beads or for the correct calculation for the number of purple beads or for the correct equation for the total number of beads (removing the denominators) or for the correct equation for the number of purple beads (removing the denominators). A value in quotation marks in the printed scheme is written here as their value, meaning the candidate's own earlier value may be used.
    3636A1cao. Working not required, so correct answer scores full marks (unless from obvious incorrect working)

    Full marks: 3/3

    Question 12, Calculator allowed

    Multiply out and simplify 3x(2x+5)(7x4)3x(2x + 5)(7x - 4) [3 marks]

    [Total 3 marks]
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    Question 12 - Exam Solution

    Understanding the Question
    Given
    The expression 3x(2x+5)(7x4)3x(2x + 5)(7x - 4)
    Three factors multiplied together: the single term 3x3x, the bracket (2x+5)(2x + 5) and the bracket (7x4)(7x - 4).
    Find
    The same expression written without brackets, with every pair of like terms collected.
    Plan the Solution
    • Multiplication can be done in any order, so take the factors two at a time.
    • Expand (2x+5)(7x4)(2x + 5)(7x - 4) first: every term in one bracket multiplies every term in the other, which gives four products.
    • Collect the two xx terms, so the bracket becomes a quadratic with three terms.
    • Multiply that quadratic by 3x3x, one term at a time.
    • Check the result by expanding in a different order, and by substituting a number.
    Worked Solution [3 marks]
    Rule - Expanding brackets: multiply every term in one bracket by every term in the other, then collect like terms. When two single terms are multiplied, multiply the numbers and add the indices: xa×xb=xa+bx^a \times x^b = x^{a+b}.
    Step 1: expand (2x+5)(7x4)(2x + 5)(7x - 4)
    (2x+5)(7x4)=2x×7x+2x×(4)+5×7x+5×(4)(2x + 5)(7x - 4) = 2x \times 7x + 2x \times (-4) + 5 \times 7x + 5 \times (-4)
    =14x28x+35x20= 14x^2 - 8x + 35x - 20
    (Reason: Each term in the first bracket multiplies each term in the second, so there are four products. The signs travel with the terms: 2x×(4)=8x2x \times (-4) = -8x and 5×(4)=205 \times (-4) = -20.)
    Step 2: collect the like terms inside the bracket
    8x+35x=27x-8x + 35x = 27x
    (2x+5)(7x4)=14x2+27x20(2x + 5)(7x - 4) = 14x^2 + 27x - 20
    (Reason: Only the two xx terms are alike. 14x214x^2 is the only squared term and 20-20 is the only number, so neither of them changes.)
    Step 3: multiply the quadratic by 3x3x
    3x(14x2+27x20)=3x×14x2+3x×27x3x×203x(14x^2 + 27x - 20) = 3x \times 14x^2 + 3x \times 27x - 3x \times 20
    =42x3+81x260x= 42x^3 + 81x^2 - 60x
    (Reason: Multiply the numbers and add the indices each time: 3×14=423 \times 14 = 42 and x×x2=x3x \times x^2 = x^3, so 3x×14x2=42x33x \times 14x^2 = 42x^3. Nothing can be collected now, because the three terms carry different powers of xx.)
    42x3+81x260x42x^3 + 81x^2 - 60x
    Verification
    Check 1 - expand in a different order: Take the single term into the first bracket instead: 3x(2x+5)=6x2+15x3x(2x + 5) = 6x^2 + 15x, then multiply that by (7x4)(7x - 4). (6x2+15x)(7x4)=42x324x2+105x260x(6x^2 + 15x)(7x - 4) = 42x^3 - 24x^2 + 105x^2 - 60x, which collects to 42x3+81x260x42x^3 + 81x^2 - 60x.
    Check 2 - substitute a value for xx: Put x=2x = 2 into the original expression. Then 3x=63x = 6, 2x+5=92x + 5 = 9 and 7x4=107x - 4 = 10. The original gives 6×9×10=5406 \times 9 \times 10 = 540, and the answer gives 42×8+81×460×2=54042 \times 8 + 81 \times 4 - 60 \times 2 = 540.
    Check 3 - is the answer the right shape? Each factor has degree 11, so the product has degree 33. Every term carries a factor of xx, so there is no number on its own, and the highest coefficient is 3×2×7=423 \times 2 \times 7 = 42. The answer is a cubic, its highest term is 42x342x^3, and it has no constant term.
    Mark Scheme Breakdown
    StepMarkDescriptionGot it?
    One pair of factors expanded: 3x(2x+5)=6x2+15x3x(2x + 5) = 6x^2 + 15x or 3x(7x4)=21x212x3x(7x - 4) = 21x^2 - 12x or (2x+5)(7x4)=14x28x+35x20(2x + 5)(7x - 4) = 14x^2 - 8x + 35x - 20 (14x2+27x20)(14x^2 + 27x - 20)M1An expansion with only one error. Do not award this mark for 6x2+15x+21x212x6x^2 + 15x + 21x^2 - 12x or (6x2+15x)(21x212x)(6x^2 + 15x)(21x^2 - 12x).
    (6x2+15x)(7x4)=42x324x2+105x260x(6x^2 + 15x)(7x - 4) = 42x^3 - 24x^2 + 105x^2 - 60x or (21x212x)(2x+5)=42x3+105x224x260x(21x^2 - 12x)(2x + 5) = 42x^3 + 105x^2 - 24x^2 - 60x or 3x(14x28x+35x20)=42x324x2+105x260x3x(14x^2 - 8x + 35x - 20) = 42x^3 - 24x^2 + 105x^2 - 60x or 3x(14x2+27x20)=42x3+81x260x3x(14x^2 + 27x - 20) = 42x^3 + 81x^2 - 60xM1ft dep on M1. Allow one further error.
    42x3+105x224x260x42x^3 + 105x^2 - 24x^2 - 60x with 33 of the terms correctM2An alternative to the two method marks above, not an addition to them. M2 for 33 (out of a maximum of 44) of 42x3+105x224x260x42x^3 + 105x^2 - 24x^2 - 60x. M1 for 22 correct out of a maximum of 44.
    42x3+81x260x42x^3 + 81x^2 - 60xA1cao (terms may be in any order but must be simplified) dep on M1. ISW correct factorisation, eg 3(14x3+27x220x)3(14x^3 + 27x^2 - 20x). Do not ISW incorrect simplification, eg 14x3+27x220x14x^3 + 27x^2 - 20x.
    Working not required, so a correct answer scores full marks (unless from obvious incorrect working).NoteGuidance for the whole question. This row awards nothing of its own.

    Full marks: 3/3

    Question 13, Calculator allowed

    The frequency table gives information about the times, in minutes, that 6060 visitors took to find their way through a hedge maze.

    01020304050600102030405060CumulativefrequencyTime (minutes)

    Time (t minutes)Frequency0<t10810<t201320<t301230<t401740<t50750<t603\begin{array}{|c|c|}\hline \textbf{Time}\ (t\ \textbf{minutes}) & \textbf{Frequency} \\ \hline 0 < t \leq 10 & 8 \\ \hline 10 < t \leq 20 & 13 \\ \hline 20 < t \leq 30 & 12 \\ \hline 30 < t \leq 40 & 17 \\ \hline 40 < t \leq 50 & 7 \\ \hline 50 < t \leq 60 & 3 \\ \hline \end{array}

    (a) Complete the cumulative frequency table.

    Time (t minutes)Cumulative frequency0<t100000<t200000<t300000<t400000<t500000<t60000\begin{array}{|c|c|}\hline \textbf{Time}\ (t\ \textbf{minutes}) & \textbf{Cumulative frequency} \\ \hline 0 < t \leq 10 & \phantom{000} \\ \hline 0 < t \leq 20 & \phantom{000} \\ \hline 0 < t \leq 30 & \phantom{000} \\ \hline 0 < t \leq 40 & \phantom{000} \\ \hline 0 < t \leq 50 & \phantom{000} \\ \hline 0 < t \leq 60 & \phantom{000} \\ \hline \end{array} [1 mark]

    (b) On the grid below, draw a cumulative frequency graph for your table. [2 marks]

    (c) Use your graph to find an estimate for the median time. [1 mark]

    (d) Use your graph to find an estimate for the number of these visitors who took more than 4545 minutes to find their way through the maze. [2 marks]

    (c) minutes(d)
    [Total 6 marks]
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    Question 13 - Exam Solution

    Understanding the Question
    Given
    The times, in minutes, that 6060 visitors took, grouped into six classes each of width 1010 minutes.
    The frequencies, in order, are 88, 1313, 1212, 1717, 77 and 33.
    Find
    (a) the cumulative frequency for each class (b) the cumulative frequency graph (c) an estimate of the median time (d) an estimate of how many visitors took more than 4545 minutes
    Plan the Solution
    • Add the frequencies down the table. Each running total counts every visitor who had finished by the END of that class.
    • Plot each running total against the UPPER end of its class, so the first point sits at 1010 minutes and not in the middle of the class, then join the points.
    • The median is read at half of 6060, so go across from 3030 on the cumulative frequency axis and down to the time axis.
    • For part (d), read UP from 4545 minutes to find how many had already finished, then take that away from 6060.
    Worked Solution [6 marks]
    Rule - Cumulative frequency: plot each running total against the UPPER end of its class, and estimate the median by reading across from n2\dfrac{n}{2} on the cumulative frequency axis.
    Step 1: add the frequencies down the table
    88
    8+13=218 + 13 = 21
    21+12=3321 + 12 = 33
    33+17=5033 + 17 = 50
    50+7=5750 + 7 = 57
    57+3=6057 + 3 = 60
    01020304050600102030405060CumulativefrequencyTime (minutes)53.527.545
    (Reason: Each cumulative frequency counts every visitor who had finished by the END of that class, so it is the running total of the frequency column. The last entry has to come out as 6060, the number of visitors, and that is the check that no frequency has been dropped.)
    Step 2: plot each total at the end of its class
    (10, 8)(20, 21)(30, 33)(10,\ 8) \qquad (20,\ 21) \qquad (30,\ 33)
    (40, 50)(50, 57)(60, 60)(40,\ 50) \qquad (50,\ 57) \qquad (60,\ 60)
    (Reason: Every visitor in the first class had finished by 1010 minutes, so that point goes at 1010 and not at the middle of the class. Joining the points gives the graph, and it may be started at (0, 0)(0,\ 0) because nobody had finished after 00 minutes.)
    Step 3: read the median off the graph
    602=30\dfrac{60}{2} = 30
    20+30213321×10=27.520 + \dfrac{30 - 21}{33 - 21} \times 10 = 27.5
    (Reason: Half of 6060 is 3030, so go across from 3030 on the cumulative frequency axis. The graph passes that height on the segment from (20, 21)(20,\ 21) to (30, 33)(30,\ 33), and the working finds how far along that segment it happens.)
    Step 4: read up from 45 minutes, then subtract
    50+45405040×(5750)=53.550 + \dfrac{45 - 40}{50 - 40} \times (57 - 50) = 53.5
    6054=660 - 54 = 6
    (Reason: Reading up from 4545 minutes to the graph and across to the cumulative frequency axis gives 53.553.5. A cumulative frequency counts whole visitors, so about 5454 had finished within 4545 minutes, and everyone else out of the 6060 took longer than that.)
    (a) 88, 2121, 3333, 5050, 5757, 6060(b) the six totals plotted at the ends of the classes and joined(c) 27.527.5 minutes(d) 66 visitors
    Verification
    Check 1: Add the six frequencies straight up. The last cumulative frequency has to be the number of visitors, because by 6060 minutes every visitor has finished. 8+13+12+17+7+3=608 + 13 + 12 + 17 + 7 + 3 = 60
    Check 2: Find the median from the other end of its class. The graph reaches 3333 at 3030 minutes, which overshoots by 33 visitors out of the 1212 in that class, so come back that fraction of the 1010 minutes. 3033303321×10=27.530 - \dfrac{33 - 30}{33 - 21} \times 10 = 27.5
    Check 3: Count the visitors still going instead of subtracting from 6060. Of the 77 in the class 40<t5040 < t \leq 50 the graph gives 5450=454 - 50 = 4 finished by 4545 minutes, and all 33 in the last class were still going. (5754)+3=6(57 - 54) + 3 = 6
    Mark Scheme Breakdown
    StepMarkDescriptionGot it?
    (a)B1for 88, 2121, 3333, 5050, 5757, 6060
    (b)M1ftfor at least 55 points plotted correctly at the end of the interval, or follow through from an ascending table (follow through from a table with only one arithmetic error that may be continued through the table) for all 66 points plotted consistently within each interval in the frequency table at the correct height
    (b)A1for fully correct plotting with points joined; accept a curve or line segments; accept a curve that is not joined at (0,0)(0, 0)
    (b)NoteA histogram or bar chart type graph scores zero marks unless a cumulative frequency diagram is drawn over the histogram or bar chart. Ignore any part of the graph before (10,8)(10, 8). Working is not required, so a correct answer scores full marks unless it comes from obviously incorrect working.
    (c)B1accept an answer in the range 2727 to 2828, or follow through an ascending graph
    (d)M1ftfollow through for a line going up from the xx-axis at 4545 to the line and across to the yy-axis, or for a mark on the line at the correct point, or for a correct reading from the vertical scale, for example 5454 or 53.553.5
    (d)A1accept integer value 55 or 66 or 77, or follow through from their ascending graph for an integer value
    (d)NoteWorking is not required, so a correct answer scores full marks unless it comes from obviously incorrect working.

    Full marks: 6/6

    Question 14, Calculator allowed

    The five graphs below are labelled A to E.

    AyxByxCyxDyxEyxOOOOO

    (a) State the letter of the graph that could have the equation y=5x2y = 5 - x^2 [1 mark]

    (b) State the letter of the graph that could have the equation y=2x3y = 2x^3 [1 mark]

    (a)(b)
    [Total 2 marks]
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    Question 14 - Exam Solution

    Understanding the Question
    Given
    Five sketch graphs on separate axes, labelled A to E. No scales are marked, so only the shape of each curve can be read.
    Two equations to match to a sketch: y=5x2y = 5 - x^2 and y=2x3y = 2x^3.
    Find
    (a) The letter of the graph that could have the equation y=5x2y = 5 - x^2. (b) The letter of the graph that could have the equation y=2x3y = 2x^3.
    Plan the Solution
    • Read the highest power of xx in each equation. That alone decides which family of curve it belongs to.
    • Read the sign in front of that highest power. It decides which way up a parabola sits, and which way a cubic runs.
    • Sort the five sketches into families first. Each family appears exactly once, so once the family is named the letter is forced.
    Worked Solution [2 marks]
    The highest power of xx fixes the shape. A term in x2x^2 gives a parabola, opening upwards when its coefficient is positive and downwards when it is negative. A term in x3x^3 gives a cubic, running from bottom left to top right when its coefficient is positive. A term in xx alone gives a straight line, and 1x\dfrac{1}{x} gives a curve in two branches with a break at x=0x = 0.
    Step 1: read the shape of y=5x2y = 5 - x^2
    y=5x2=x2+5y = 5 - x^2 = -x^2 + 5
    (Reason: The highest power is 22, so the curve is a parabola. The number in front of x2x^2 is 1-1, which is negative, so the parabola opens downwards: it turns at a maximum, not a minimum.)
    Step 2: test three values, then match
    5(3)2=45 - (-3)^2 = -4
    502=55 - 0^2 = 5
    532=45 - 3^2 = -4
    (Reason: The curve is below the xx-axis at x=3x = -3, above it at x=0x = 0 and below it again at x=3x = 3 - up in the middle and down at both ends. Graph B is the only sketch that does that. Graph D is a parabola as well, but it opens upwards, which needs a positive x2x^2 term.)
    Step 3: read the shape of y=2x3y = 2x^3
    2×(2)3=162 \times (-2)^3 = -16
    2×23=162 \times 2^3 = 16
    (Reason: The highest power is 33, so the curve is a cubic. The two values either side of the yy-axis are the same size but opposite in sign, so the curve sits below the xx-axis on the left and above it on the right. The coefficient 22 is positive, so it runs upwards from left to right.)
    Step 4: match the cubic to a sketch
    2×03=02 \times 0^3 = 0
    (Reason: The curve must pass through the origin, which rules out graph A - it has a break at x=0x = 0 and never meets either axis - and rules out graph E, which is straight and crosses the yy-axis above the origin. Both parabolas are out too, because a parabola gives the same value at xx and at x-x while a cubic changes sign. Graph C is the one left: it climbs from the bottom left, flattens at the origin and rises steeply to the top right.)
    (a) Graph B(b) Graph C
    Verification
    Check 1: Test the symmetry for part (a). Put x=1x = 1 and x=1x = -1 into y=5x2y = 5 - x^2. 512=45 - 1^2 = 4 and 5(1)2=45 - (-1)^2 = 4 - the same height either side of the yy-axis. Only B and D have that symmetry, and of those two only B turns at a maximum.
    Check 2: Test part (b) the same way. Put x=1x = 1 and x=1x = -1 into y=2x3y = 2x^3. 2×13=22 \times 1^3 = 2 and 2×(1)3=22 \times (-1)^3 = -2 - equal in size but opposite in sign, so the curve crosses from below the xx-axis to above it as it passes through the origin. Graph C is the only sketch shaped that way.
    Check 3: Count the families. The five sketches are five different shapes: a two-branch curve, a downward parabola, a cubic, an upward parabola and a straight line. A downward parabola and a cubic each appear exactly once, so the two answers are forced and no letter is used twice.
    Mark Scheme Breakdown
    StepMarkDescriptionGot it?
    (a)B1B - cao
    (b)B1C - cao

    Full marks: 2/2

    Question 15, Calculator allowed

    Simplify fully
    (2a310a7c2)3\left( \dfrac{2a^{3}}{10a^{7}c^{2}} \right)^{-3} [3 marks]

    [Total 3 marks]
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    Question 15 - Exam Solution

    Understanding the Question
    Given
    The expression (2a310a7c2)3\left( \dfrac{2a^{3}}{10a^{7}c^{2}} \right)^{-3}
    One fraction in aa and cc, raised to the power 3-3.
    Find
    The same expression written as simply as possible. Expect one number multiplied by one power of aa and one power of cc.
    Plan the Solution
    • Tidy the inside of the bracket first: cancel the numbers, then subtract the indices of aa with xmxn=xmn\dfrac{x^{m}}{x^{n}} = x^{m-n}.
    • Leave the index outside the bracket until last. It is negative, so it turns the fraction over: raising to 3-3 is the same as flipping the fraction and raising to 33.
    • Cube each factor separately. The number in front is a factor too, so it is cubed as well as the letters.
    Worked Solution [3 marks]
    Rule - Index laws: xmxn=xmn\dfrac{x^{m}}{x^{n}} = x^{m-n}, (xm)n=xmn(x^{m})^{n} = x^{mn} and xn=1xnx^{-n} = \dfrac{1}{x^{n}}.
    Step 1: Simplify inside the bracket
    2a310a7c2=210×a3a7×1c2\dfrac{2a^{3}}{10a^{7}c^{2}} = \dfrac{2}{10} \times \dfrac{a^{3}}{a^{7}} \times \dfrac{1}{c^{2}}
    210=15\dfrac{2}{10} = \dfrac{1}{5}
    a3a7=a37=a4=1a4\dfrac{a^{3}}{a^{7}} = a^{3-7} = a^{-4} = \dfrac{1}{a^{4}}
    2a310a7c2=15a4c2\dfrac{2a^{3}}{10a^{7}c^{2}} = \dfrac{1}{5a^{4}c^{2}}
    (Reason: Dividing powers of the same letter subtracts the indices, and a4a^{-4} is another way of writing 1a4\dfrac{1}{a^{4}}, so both letters end up in the denominator.)
    Step 2: Turn the fraction over to deal with the negative index
    (15a4c2)3=(5a4c2)3\left( \dfrac{1}{5a^{4}c^{2}} \right)^{-3} = \left( 5a^{4}c^{2} \right)^{3}
    (Reason: A negative index means the reciprocal: y3=1y3y^{-3} = \dfrac{1}{y^{3}}, so a fraction raised to 3-3 is that fraction turned upside down and raised to 33. Flipping 15a4c2\dfrac{1}{5a^{4}c^{2}} leaves 5a4c25a^{4}c^{2}.)
    Step 3: Cube every factor inside the bracket
    (5a4c2)3=53×a4×3×c2×3\left( 5a^{4}c^{2} \right)^{3} = 5^{3} \times a^{4 \times 3} \times c^{2 \times 3}
    53×a4×3×c2×3=125a12c65^{3} \times a^{4 \times 3} \times c^{2 \times 3} = 125a^{12}c^{6}
    (Reason: A power outside a bracket multiplies every index inside it, so a4a^{4} becomes a12a^{12} and c2c^{2} becomes c6c^{6}. The number in front is a factor of the bracket like the letters are, so it is raised to the power too.)
    125a12c6125a^{12}c^{6}
    Verification
    Check 1: Put a=2a = 2 and c=3c = 3 into the original expression, and into the answer, and compare the two values. Inside the bracket 2×810×128×9=1611520=1720\dfrac{2 \times 8}{10 \times 128 \times 9} = \dfrac{16}{11\,520} = \dfrac{1}{720}, so the original is 7203=373248000720^{3} = 373\,248\,000, and the answer gives 125×4096×729=373248000125 \times 4096 \times 729 = 373\,248\,000.
    Check 2: Work backwards. Take the cube root of the answer and check it is the reciprocal of the bracket that Step 1 produced. 125a12c63=5a4c2\sqrt[3]{125a^{12}c^{6}} = 5a^{4}c^{2}, and 15a4c2\dfrac{1}{5a^{4}c^{2}} is exactly the simplified bracket, so the negative index has been undone correctly.
    Check 3: Take a different order of working: turn the fraction over first, cube the top and the bottom without simplifying anything, and only then cancel. (10a7c2)3(2a3)3=1000a21c68a9=125a12c6\dfrac{(10a^{7}c^{2})^{3}}{(2a^{3})^{3}} = \dfrac{1000a^{21}c^{6}}{8a^{9}} = 125a^{12}c^{6}, since 10008=125\dfrac{1000}{8} = 125 and a219=a12a^{21-9} = a^{12}.
    Mark Scheme Breakdown
    StepMarkDescriptionGot it?
    Fully simplified: 125a12c6125a^{12}c^{6}B3for 125a12c6125a^{12}c^{6} oe, eg 125a12c6\dfrac{125a^{12}}{c^{-6}} or 125c6a12\dfrac{125c^{6}}{a^{-12}} or 125a12c6\dfrac{125}{a^{-12}c^{-6}} or a121251c6\dfrac{a^{12}}{125^{-1}c^{-6}} or 11251a12c6\dfrac{1}{125^{-1}a^{-12}c^{-6}} or a12c61251\dfrac{a^{12}c^{6}}{125^{-1}}
    Two correct termsB2for 22 correct terms (Allow eg 125a12125a^{12} or 125c6125c^{6} or ka12c6ka^{12}c^{6} as long as not added to any other terms)
    One correct termB1for one correct term (allow eg a12a^{12} or a12c6a^{-12}c^{6} or 11251\dfrac{1}{125^{-1}} or 1000a21c68a9\dfrac{1000a^{21}c^{6}}{8a^{9}} as long as not added to any other terms)

    Full marks: 3/3

    Question 16, Calculator allowed

    Rearrange the formula
    c=t2+378t2c = \dfrac{t^2 + 3}{7 - 8t^2}
    to make tt the subject. [4 marks]

    [Total 4 marks]
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    Question 16 - Exam Solution

    Understanding the Question
    Given
    The formula c=t2+378t2c = \dfrac{t^2 + 3}{7 - 8t^2}.
    The letter tt appears in the numerator and in the denominator, and only ever as t2t^2.
    Find
    A formula for tt in terms of cc.
    Plan the Solution
    • Multiply both sides by 78t27 - 8t^2 so that no tt is left underneath a fraction bar.
    • Gather every term containing t2t^2 on one side and everything else on the other.
    • Take t2t^2 out as a common factor, then divide by the bracket that is left.
    • Square root last, and keep both signs.
    Worked Solution [4 marks]
    Rule - Changing the subject: clear the fraction, collect every term containing the new subject on one side, factorise it out, then undo what is left around it. Here the new subject appears as t2t^2, so the last step is a square root and both signs are kept.
    Step 1: multiply both sides by the denominator
    c(78t2)=t2+3c(7 - 8t^2) = t^2 + 3
    7c8ct2=t2+37c - 8ct^2 = t^2 + 3
    (Reason: (Reason: while tt sits underneath a fraction bar nothing can be collected, so the fraction is cleared first. Multiplying out the bracket turns the left-hand side into the two terms 7c7c and 8ct2-8ct^2.))
    Step 2: collect the t2t^2 terms on one side
    7c3=t2+8ct27c - 3 = t^2 + 8ct^2
    (Reason: (Reason: add 8ct28ct^2 to both sides and take the 33 across, so that the two t2t^2 terms end up together on the right and the terms with no tt in them end up on the left.))
    Step 3: factorise t2t^2 out
    7c3=t2(1+8c)7c - 3 = t^2(1 + 8c)
    (Reason: (Reason: t2t^2 is a common factor of t2t^2 and 8ct28ct^2, and taking it out is what turns two t2t^2 terms into one.))
    Step 4: divide, then square root
    t2=7c31+8ct^2 = \dfrac{7c - 3}{1 + 8c}
    t=±7c31+8ct = \pm\sqrt{\dfrac{7c - 3}{1 + 8c}}
    (Reason: (Reason: dividing by the bracket leaves t2t^2 on its own. Squaring hides a sign, so undoing it gives two values: both tt and t-t lead back to the same cc.))
    t=±7c31+8ct = \pm\sqrt{\dfrac{7c - 3}{1 + 8c}}
    Verification
    Check 1 - put t=1t = 1through both formulas: The formula on the paper gives 1+378=41=4\dfrac{1 + 3}{7 - 8} = \dfrac{4}{-1} = -4, so c=4c = -4. Feeding c=4c = -4 into the rearranged formula gives 7×(4)31+8×(4)=3131=1\dfrac{7 \times (-4) - 3}{1 + 8 \times (-4)} = \dfrac{-31}{-31} = 1, and the square root of that is 11 again.
    Check 2 - work the other way, from cc back to tt: Put c=1c = 1 into the rearranged formula: 731+8=49\dfrac{7 - 3}{1 + 8} = \dfrac{4}{9}, so t=±23t = \pm\dfrac{2}{3}. Putting t2=49t^2 = \dfrac{4}{9} back into the formula on the paper, and multiplying the top and the bottom by 99, gives 4+276332=3131=1\dfrac{4 + 27}{63 - 32} = \dfrac{31}{31} = 1, the value of cc we started with.
    Check 3 - why both signs are kept: The formula uses tt only as t2t^2, so tt and t-t have to give the same cc. t=1t = -1 gives 1+378=4\dfrac{1 + 3}{7 - 8} = -4, the same value as t=1t = 1, so an answer carrying one sign only would lose half of it.
    Mark Scheme Breakdown
    StepMarkDescriptionGot it?
    7c8ct2=t2+37c - 8ct^2 = t^2 + 3 oeM1For multiplying both sides by the denominator and expanding the brackets.
    7c3=t2+8ct27c - 3 = t^2 + 8ct^2 oe or 8ct2t2=37c-8ct^2 - t^2 = 3 - 7c oeM1Follow through, dependent on 2 terms in t2t^2 and 2 other terms. For collecting the t2t^2 terms on one side and the other terms on the other side.
    7c3=t2(1+8c)7c - 3 = t^2(1 + 8c) oe or t2(8c1)=37ct^2(-8c - 1) = 3 - 7c oeM1Follow through, dependent on the previous M1. For factorising for t2t^2.
    t=(±)7c31+8ct = (\pm)\sqrt{\dfrac{7c - 3}{1 + 8c}}A1Or equivalent, for example t=(±)37c8c1t = (\pm)\sqrt{\dfrac{3 - 7c}{-8c - 1}} or t=(±)(7c31+8c)12t = (\pm)\left(\dfrac{7c - 3}{1 + 8c}\right)^{\dfrac{1}{2}} or t=(±)(7c31+8c)0.5t = (\pm)\left(\dfrac{7c - 3}{1 + 8c}\right)^{0.5}.
    NBNoteTo award the A1 we must see t=(±)7c31+8ct = (\pm)\sqrt{\dfrac{7c - 3}{1 + 8c}} in the working if (±)7c31+8c(\pm)\sqrt{\dfrac{7c - 3}{1 + 8c}} alone is given as the answer.
    WorkingNoteWorking is not required, so a correct answer scores full marks unless it comes from obviously incorrect working.

    Full marks: 4/4

    Question 17, Calculator allowed

    y=4x3+5x2+2xy = 4x^3 + 5x^2 + 2x

    (a) Find dydx\dfrac{dy}{dx} [2 marks]

    (b) Work out the coordinates of the turning points on the curve with equation y=4x3+5x2+2xy = 4x^3 + 5x^2 + 2x
    You must show clear algebraic working. [4 marks]

    (a)(b)
    [Total 6 marks]
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    Question 17 - Exam Solution

    Understanding the Question
    Given
    y=4x3+5x2+2xy = 4x^3 + 5x^2 + 2x
    A cubic, so the derivative is a quadratic and the curve can have up to two turning points.
    Find
    (a) dydx\dfrac{dy}{dx} (b) the coordinates of the turning points, so an xx and a yy for each one
    Plan the Solution
    • Differentiate term by term: multiply each term by its power, then take one off the power.
    • A turning point is where the curve is momentarily flat, so set dydx=0\dfrac{dy}{dx} = 0 and solve.
    • Every coefficient of the derivative is even, so take the factor 22 out before factorising the quadratic.
    • Put each root back into the original cubic to get its yy value. The derivative gives gradients, not heights.
    Worked Solution [6 marks]
    Rule - Turning points: differentiate, set dydx=0\dfrac{dy}{dx} = 0, solve for xx, then substitute each xx back into the original equation to get yy.
    Step 1: Differentiate term by term
    y=4x3+5x2+2xy = 4x^3 + 5x^2 + 2x
    dydx=3×4x2+2×5x+2\dfrac{dy}{dx} = 3 \times 4x^{2} + 2 \times 5x + 2
    dydx=12x2+10x+2\dfrac{dy}{dx} = 12x^2 + 10x + 2
    (Reason: The power rule: multiply by the power, then take one off it. So 4x34x^3 gives 12x212x^2, 5x25x^2 gives 10x10x, and 2x2x gives 22. That is part (a) answered.)
    Step 2: Set the gradient equal to zero
    12x2+10x+2=012x^2 + 10x + 2 = 0
    2(6x2+5x+1)=02(6x^2 + 5x + 1) = 0
    6x2+5x+1=06x^2 + 5x + 1 = 0
    (Reason: At a turning point the tangent is horizontal, so the gradient is 00. Every coefficient is even, so dividing through by 22 leaves smaller numbers to factorise.)
    Step 3: Factorise and solve for xx
    6x2+5x+1=(3x+1)(2x+1)6x^2 + 5x + 1 = (3x + 1)(2x + 1)
    (3x+1)(2x+1)=0(3x + 1)(2x + 1) = 0
    3x+1=0    x=133x + 1 = 0 \implies x = -\dfrac{1}{3}
    2x+1=0    x=122x + 1 = 0 \implies x = -\dfrac{1}{2}
    (Reason: Split the 66 as 3×23 \times 2 and the 11 as 1×11 \times 1; the cross terms 3x+2x3x + 2x rebuild the middle term 5x5x. A product is zero only when one of its brackets is zero.)
    Step 4: Substitute x=12x = -\dfrac{1}{2} into the original equation
    y=4(12)3+5(12)2+2(12)y = 4\left(-\dfrac{1}{2}\right)^{3} + 5\left(-\dfrac{1}{2}\right)^{2} + 2\left(-\dfrac{1}{2}\right)
    y=12+541=14y = -\dfrac{1}{2} + \dfrac{5}{4} - 1 = -\dfrac{1}{4}
    (Reason: The height comes from the original cubic, never from the derivative. Cubing a negative keeps it negative, while squaring it makes it positive, so the first term is 12-\dfrac{1}{2} and the second is +54+\dfrac{5}{4}.)
    Step 5: Substitute x=13x = -\dfrac{1}{3} into the original equation
    y=4(13)3+5(13)2+2(13)y = 4\left(-\dfrac{1}{3}\right)^{3} + 5\left(-\dfrac{1}{3}\right)^{2} + 2\left(-\dfrac{1}{3}\right)
    y=427+5923=727y = -\dfrac{4}{27} + \dfrac{5}{9} - \dfrac{2}{3} = -\dfrac{7}{27}
    (Reason: The same substitution again. Writing all three terms over a denominator of 2727 keeps the fraction arithmetic exact.)
    (a) dydx=12x2+10x+2\dfrac{dy}{dx} = 12x^2 + 10x + 2(b) (12, 14)\left(-\dfrac{1}{2},\ -\dfrac{1}{4}\right) and (13, 727)\left(-\dfrac{1}{3},\ -\dfrac{7}{27}\right)
    Verification
    Check 1: Expand the factorisation back out. (3x+1)(2x+1)(3x + 1)(2x + 1) should rebuild 6x2+5x+16x^2 + 5x + 1, and doubling every term should rebuild part (a). 2(6x2+5x+1)=12x2+10x+22(6x^2 + 5x + 1) = 12x^2 + 10x + 2
    Check 2: Put each root back into the derivative. The gradient must come out as exactly 00 at a turning point. 12(12)2+10(12)+2=012\left(-\dfrac{1}{2}\right)^{2} + 10\left(-\dfrac{1}{2}\right) + 2 = 0 and 12(13)2+10(13)+2=012\left(-\dfrac{1}{3}\right)^{2} + 10\left(-\dfrac{1}{3}\right) + 2 = 0
    Check 3: The two roots of 6x2+5x+1=06x^2 + 5x + 1 = 0 must add to 56-\dfrac{5}{6} and multiply to 16\dfrac{1}{6}. 1213=56-\dfrac{1}{2} - \dfrac{1}{3} = -\dfrac{5}{6} and (12)(13)=16\left(-\dfrac{1}{2}\right)\left(-\dfrac{1}{3}\right) = \dfrac{1}{6}
    Check 4: Redo the second turning point in decimals on the calculator. x0.3333x \approx -0.3333 gives a height just below the first turning point, which is what a local minimum sitting to the right of a local maximum should do. 7270.2593-\dfrac{7}{27} \approx -0.2593, lower than 14=0.25-\dfrac{1}{4} = -0.25
    Mark Scheme Breakdown
    StepMarkDescriptionGot it?
    (a) Two of 12x2+10x+212x^2 + 10x + 2M1for differentiating 2 or 3 terms correctly
    (a) 12x2+10x+212x^2 + 10x + 2A1for all 3 terms correct
    (b) (3x+1)(4x+2) (=0)(3x + 1)(4x + 2)\ (= 0) or (6x+2)(2x+1)(=0)(6x + 2)(2x + 1)(= 0) or 2(3x+1)(2x+1) (=0)2(3x + 1)(2x + 1)\ (= 0) or (3x+1)(2x+1)(=0)(3x + 1)(2x + 1)(= 0) or 10±1024×12×22×12\dfrac{-10 \pm \sqrt{10^2 - 4 \times 12 \times 2}}{2 \times 12} or 5±524×6×12×6\dfrac{-5 \pm \sqrt{5^2 - 4 \times 6 \times 1}}{2 \times 6} or 12[(x+1024)2(1024)2]+2 (=0)12\left[\left(x + \dfrac{10}{24}\right)^{2} - \left(\dfrac{10}{24}\right)^{2}\right] + 2\ (= 0) oe or 6[(x+512)2(512)2]+1 (=0)6\left[\left(x + \dfrac{5}{12}\right)^{2} - \left(\dfrac{5}{12}\right)^{2}\right] + 1\ (= 0) oeM1ft dep on M1 for a correct method to solve their 3 term quadratic equation (with at least 2 correct coefficients) using any correct method (if factorising, allow brackets which expanded give 2 out of 3 terms correct) (if using formula allow one sign error and some simplification - allow as far as 10±1009624\dfrac{-10 \pm \sqrt{100 - 96}}{24}) Derivative must be a 3 term quadratic for this M mark
    NB Can be implied by answers of (x=)12(x =) -\dfrac{1}{2} and (x=)13(x =) -\dfrac{1}{3}
    (b) 12-\dfrac{1}{2}, 13-\dfrac{1}{3}A1oe dep on previous M1. Allow 0.33(333)-0.33(333) or 0.3˙-0.\dot{3} for correct xx values
    (b) (y=)4×(12)3+5×(12)2+2(12) (=14)(y =) 4 \times \left(-\dfrac{1}{2}\right)^{3} + 5 \times \left(-\dfrac{1}{2}\right)^{2} + 2\left(-\dfrac{1}{2}\right)\ \left(= -\dfrac{1}{4}\right) or (y=)4×(13)3+5×(13)2+2(13) (=727)(y =) 4 \times \left(-\dfrac{1}{3}\right)^{3} + 5 \times \left(-\dfrac{1}{3}\right)^{2} + 2\left(-\dfrac{1}{3}\right)\ \left(= -\dfrac{7}{27}\right)M1ft dep on previous M1 for substituting at least one xx value into yy
    NB Can be implied by one correct value of yy
    (b) Working required. (12, 14)\left(-\dfrac{1}{2},\ -\dfrac{1}{4}\right), (13, 727)\left(-\dfrac{1}{3},\ -\dfrac{7}{27}\right)A1oe dep on M1 for correct coordinates (0.5, 0.25)(-0.5,\ -0.25), (0.33, 0.25(9))(-0.33,\ -0.25(9 \ldots))

    Full marks: 6/6

    Question 18, Calculator allowed

    Show, using algebra, that 0.7˙02˙=26370.\dot{7}0\dot{2} = \dfrac{26}{37} [2 marks]

    [Total 2 marks]
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    Question 18 - Exam Solution

    Understanding the Question
    Given
    The recurring decimal 0.7˙02˙0.\dot{7}0\dot{2}. The dots sit on the 77 and on the 22, so the block 702702 repeats for ever: 0.7027027020.702702702\ldots
    The fraction it is claimed to equal: 2637\dfrac{26}{37}
    Find
    Show that 0.7˙02˙0.\dot{7}0\dot{2} is exactly 2637\dfrac{26}{37}. The working is the answer here, so there is nothing to write on an answer line, and the working must be algebra - a solution with no algebra is capped at 1 mark.
    Plan the Solution
    • Give the recurring decimal a letter, so that there is something to do algebra with.
    • Count the digits in the repeating block: 702702 is 33 digits long, so the multiplier is 103=100010^{3} = 1000.
    • Write the two lines under each other and subtract. The endless tails are identical, so they cancel and leave a whole number.
    • Divide to reach a fraction, then cancel that fraction to its lowest terms.
    Worked Solution [2 marks]
    Rule - Recurring decimal to fraction: call the decimal xx. If the repeating block is nn digits long, multiply by 10n10^{n} and subtract xx. The identical tails cancel, and (10n1)x(10^{n} - 1)x is left equal to a whole number.
    Step 1: give the decimal a letter
    x=0.7˙02˙=0.702702702x = 0.\dot{7}0\dot{2} = 0.702702702\ldots
    (Reason: Algebra needs something to hold on to, so the decimal is called xx. The dots say the block 702702 repeats without end, so the digits after the point never stop and never change pattern.)
    Step 2: multiply by 10001000
    1000x=702.7˙02˙=702.7027021000x = 702.\dot{7}0\dot{2} = 702.702702\ldots
    (Reason: The repeating block is 33 digits long, so multiplying by 103=100010^{3} = 1000 slides the point past exactly one whole block. The tail left after the point is then the same tail as before, digit for digit.)
    Step 3: subtract the two lines
    1000xx=702.7027020.7027021000x - x = 702.702702\ldots - 0.702702\ldots
    999x=702999x = 702
    (Reason: Both lines carry exactly the same endless tail, so subtracting wipes it out and leaves a whole number. Choosing the multiplier to match the block length is what makes that happen, and it is what earns the first mark.)
    Step 4: divide, then cancel
    x=702999x = \dfrac{702}{999}
    702=27×26702 = 27 \times 26
    999=27×37999 = 27 \times 37
    702999=2637\dfrac{702}{999} = \dfrac{26}{37}
    (Reason: Divide both sides by 999999. The highest common factor of 702702 and 999999 is 2727, so dividing the top and the bottom by 2727 puts the fraction in its lowest terms. Cancelling by anything smaller leaves the fraction unfinished, and the second mark is for the completion.)
    0.7˙02˙=26370.\dot{7}0\dot{2} = \dfrac{26}{37} as required
    Verification
    Check 1: Two fractions are equal exactly when their cross products match. Multiply 2626 by 999999, then multiply 3737 by 702702. 26×999=2597426 \times 999 = 25\,974 and 37×702=2597437 \times 702 = 25\,974
    Check 2: Start again with a different pair of lines, 10000x10000x and 10x10x. Their tails match too, so subtracting gives 9990x=70209990x = 7020. 70209990=2637\dfrac{7020}{9990} = \dfrac{26}{37} - the same fraction, from different multipliers
    Check 3: Go the other way and divide 2626 by 3737 by hand. The remainders come out 11, 1010, 2626 - and 2626 is where the division started. Once a remainder repeats the digits must repeat too, so the quotient is 0.7027027020.702702702\ldots, which is 0.7˙02˙0.\dot{7}0\dot{2}
    Mark Scheme Breakdown
    StepMarkDescriptionGot it?
    eg (1000x=)702.702(1000x =) 702.702\ldots and (x=)0.702(x =) 0.702\ldotsM1for 22 recurring decimals that when subtracted give a whole number or terminating decimal with intention to subtract (ie give 702702 or 70207020 or 7020070200 etc)
    eg (1000x=)702.702(1000x =) 702.702\ldots and (x=)0.702(x =) 0.702\ldots
    or (10000x=)7027.02(10000x =) 7027.02\ldots and (10x=)7.02(10x =) 7.02\ldots
    or (100000x=)70270.20(100000x =) 70270.20\ldots and (100x=)70.20(100x =) 70.20\ldots
    with intention to subtract
    xx is not required to award this mark
    (if recurring dots not shown in both numbers then showing at least one of the numbers to at least 66sf)
    NB Accept bar notation for dot notation to indicate recurring decimals
    eg 1000xx=702.7020.702=7021000x - x = 702.702\ldots - 0.702\ldots = 702 (999x=702)(999x = 702) and 702999=2637\dfrac{702}{999} = \dfrac{26}{37}
    or 10000x10x=7027.027.02=702010000x - 10x = 7027.02\ldots - 7.02\ldots = 7020 (9990x=7020)(9990x = 7020) and 70209990=2637\dfrac{7020}{9990} = \dfrac{26}{37}
    or 100000x100x=70270.2070.20=70200100000x - 100x = 70270.20\ldots - 70.20\ldots = 70200 (99900x=70200)(99900x = 70200) and 7020099900=2637\dfrac{70200}{99900} = \dfrac{26}{37}
    Answer column: shown
    A1for completion to 2637\dfrac{26}{37} dep on M1 and must use algebra for this final mark to be awarded
    No algebra used gets a maximum of 1 mark
    Working requiredNoteThe fraction is printed in the question, so a solution that only restates it earns nothing: the working is what is being marked.

    Full marks: 2/2

    Question 19, Calculator allowed

    Solve the inequality 4x2+4x15<04x^2 + 4x - 15 < 0
    You must show clear algebraic working. [3 marks]

    [Total 3 marks]
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    Question 19 - Exam Solution

    Understanding the Question
    Given
    The quadratic inequality 4x2+4x15<04x^2 + 4x - 15 < 0.
    The coefficient of x2x^2 is 44, which is positive, so y=4x2+4x15y = 4x^2 + 4x - 15 is a parabola opening upwards: it dips below the axis once and comes back up.
    The sign is strict. <0< 0 means negative, so a value of xx that makes the expression exactly 00 is not part of the solution.
    Find
    Every value of xx for which 4x2+4x154x^2 + 4x - 15 is negative, written as one inequality. Clear algebraic working is asked for, so the two critical values must be reached by factorising, by the formula or by completing the square. Both answer marks depend on that method mark, so critical values written down with nothing behind them score nothing at all.
    Plan the Solution
    • Solve the equation 4x2+4x15=04x^2 + 4x - 15 = 0 first. Its two solutions are the critical values, where the curve crosses the xx-axis and where the expression can change sign.
    • Factorise by splitting the middle term: look for two numbers with product 4×(15)=604 \times (-15) = -60 and sum 44.
    • Decide which side of the critical values the curve sits below the axis. With a positive x2x^2 coefficient that is the region between them, and one test value confirms it.
    • Write the answer as a single double inequality, with strict signs at both ends.
    Worked Solution [3 marks]
    Rule - Quadratic inequality: solve the equation to find the critical values, then choose the region. For ax2+bx+c<0ax^2 + bx + c < 0 with a>0a > 0 the expression is negative between the two roots and positive outside them.
    Step 1: solve the equation 4x2+4x15=04x^2 + 4x - 15 = 0
    4x2+4x15=04x^2 + 4x - 15 = 0
    4×(15)=604 \times (-15) = -60
    10×(6)=6010 \times (-6) = -60
    10+(6)=410 + (-6) = 4
    4x2+10x6x15=04x^2 + 10x - 6x - 15 = 0
    2x(2x+5)3(2x+5)=02x(2x + 5) - 3(2x + 5) = 0
    (2x+5)(2x3)=0(2x + 5)(2x - 3) = 0
    (Reason: The expression can only change sign where it is zero, so the equation comes first. To factorise it, look for two numbers whose product is 4×(15)=604 \times (-15) = -60 and whose sum is 44: they are 1010 and 6-6. Splitting the middle term with them leaves the common bracket (2x+5)(2x + 5) to take out. This is the method mark, and the quadratic formula or completing the square would earn it just as well.)
    Step 2: read the critical values off the brackets
    2x+5=0    x=52=2.52x + 5 = 0 \implies x = -\dfrac{5}{2} = -2.5
    2x3=0    x=32=1.52x - 3 = 0 \implies x = \dfrac{3}{2} = 1.5
    (Reason: A product is zero only when one of its factors is zero, so each bracket gives one critical value. These are the two places where the curve y=4x2+4x15y = 4x^2 + 4x - 15 meets the xx-axis, and they are what the first answer mark is for.)
    Step 3: decide which side of the critical values is negative
    4×02+4×015=154 \times 0^2 + 4 \times 0 - 15 = -15
    4×22+4×215=94 \times 2^2 + 4 \times 2 - 15 = 9
    4×(3)2+4×(3)15=94 \times (-3)^2 + 4 \times (-3) - 15 = 9
    (Reason: The critical values 2.5-2.5 and 1.51.5 cut the number line into three pieces, and the expression keeps one sign right across each piece. Testing x=0x = 0 from between them gives 15-15, which is negative. Testing x=2x = 2 and x=3x = -3 from outside gives 99 both times, which is positive. That is exactly the shape a positive x2x^2 coefficient forces: below the axis between the roots, above it either side.)
    Step 4: write the solution as one inequality
    2.5<x<1.5-2.5 < x < 1.5
    (Reason: The negative piece is the one between the critical values, so xx has to be greater than 2.5-2.5 and less than 1.51.5 at the same time, and those two conditions are written as one double inequality. Both signs stay strict, because at 2.5-2.5 and at 1.51.5 the expression is 00, and the question asks for less than 00. Turning the answer inside out, as x<2.5x < -2.5 or x>1.5x > 1.5, would describe where the expression is positive instead.)
    2.5<x<1.5-2.5 < x < 1.5 (equivalently 52<x<32-\dfrac{5}{2} < x < \dfrac{3}{2})
    Verification
    Check 1: Take two values from inside the interval, x=1x = 1 and x=2x = -2, and work the expression out for each. 4+415=74 + 4 - 15 = -7 and 16815=716 - 8 - 15 = -7, both negative, so both values belong
    Check 2: Take one value from beyond each end, x=2x = 2 and x=3x = -3, so that both sides outside the interval are tested. 16+815=916 + 8 - 15 = 9 and 361215=936 - 12 - 15 = 9, both positive, so neither value belongs
    Check 3: Multiply the brackets out again and compare the result with the expression the question prints. (2x+5)(2x3)=4x26x+10x15=4x2+4x15(2x + 5)(2x - 3) = 4x^2 - 6x + 10x - 15 = 4x^2 + 4x - 15
    Check 4: Reach the two critical values a completely different way, with the quadratic formula, and see whether they come back the same. 4±16+2408=4±168\dfrac{-4 \pm \sqrt{16 + 240}}{8} = \dfrac{-4 \pm 16}{8}, giving 1.51.5 and 2.5-2.5 again
    Mark Scheme Breakdown
    StepMarkDescriptionGot it?
    (2x3)(2x+5)(2x - 3)(2x + 5)
    or 4±424×4×152×4\dfrac{-4 \pm \sqrt{4^2 - 4 \times 4 \times -15}}{2 \times 4}
    or 4[(x+12)2(12)2]15(=0)4\left[\left(x + \dfrac{1}{2}\right)^2 - \left(\dfrac{1}{2}\right)^2\right] - 15 \, (= 0)
    or 4(x+42×4)2424×4+15(=0)4\left(x + \dfrac{4}{2 \times 4}\right)^2 - \dfrac{4^2}{4 \times 4} + -15 \, (= 0)
    M1for a correct method to solve the quadratic equation 4x2+4x15=04x^2 + 4x - 15 = 0
    Allow (4x6)(x+2.5)(4x - 6)(x + 2.5) or (4x+10)(x1.5)(4x + 10)(x - 1.5) or (4x6)(4x+10)(4x - 6)(4x + 10) leading to (x1.5)(x+2.5)(x - 1.5)(x + 2.5) or (4x6)(4x+10)(4x - 6)(4x + 10) leading to correct values of xx
    Do not allow (x1.5)(x+2.5)(x - 1.5)(x + 2.5) without previous working
    (If using formula allow some simplification - allow as far as 4±16+2408\dfrac{-4 \pm \sqrt{16 + 240}}{8})
    1.5,2.51.5, -2.5 oeA1oe dep on M1
    Answer column: 2.5<x<1.5-2.5 < x < 1.5A1oe dep on M1
    Allow x>2.5x > -2.5 (and) x<1.5x < 1.5 oe
    Allow any variable as long as used all the way through
    Where the three marks fallNoteThe two answer marks sit in separate rows and both depend on the method mark, so a solution that states the critical values with no method behind them - the (x1.5)(x+2.5)(x - 1.5)(x + 2.5) case the first row rules out - scores nothing rather than one. The second answer mark is for the region and not for the numbers, so a candidate who reaches 1.51.5 and 2.5-2.5 and then writes x<2.5x < -2.5 or x>1.5x > 1.5 keeps the first answer mark and loses the second: that is the region where the expression is positive.

    Full marks: 3/3

    Continue to questions 20 to 26

    The remaining 7 questions, with the same full worked solutions and mark schemes

    Keep revising

    That is part two of three. Read what the IGCSE is and how it is graded, or compare Edexcel 4MA1 with Cambridge 0580 if you are still choosing a board. Check the IGCSE grade boundaries to set your target, and if the exam is close, the four-week IGCSE Maths revision plan sets out what to do week by week.

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