Printable · GCSE Foundation · ages 14-16
Algebra worksheet — GCSE Foundation
Fifteen questions across the algebra statements at Foundation tier. Choose the non-calculator filter to rehearse Paper 1, which counts for a third of the marks.
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Algebra worksheet — GCSE Foundation
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- 1.Priya buys b balloons for a party. Each balloon costs 15p. Write down an expression for the total cost, in pence.
- 2.y = 5 − 2x. Work out the value of x when y = 11.
- 3.A point lies on the y-axis. What can be said about the x-coordinate of that point?
- 4.A straight line has equation y = 4 − 3x. Work out the gradient of the line.
- 5.The first four terms of a sequence are 11, 18, 25, 32. Ravi thinks the nth term is 7n. Work out the correct expression for the nth term.
- 6.Work out the value of 3x² − 4x when x = −2.
- 7.Which of these equations describes a vertical line?
- 8.Kai writes the expression 8 − 3x + 5x² and says it has three terms. Ryan says it only has two terms because a number on its own is not a term. Work out the correct number of terms in the expression.
- 9.An equation has exactly one value of x that makes it true, but an identity is true for every value of x. Which of these best explains why 3x + 5 = 20 is an equation rather than an identity?
- 10.A number, n, is tripled and then 4.5 is added. The result is 22.5. Form an equation and solve it to find n.
- 11.Which of these quadratic graphs does NOT cross the x-axis at all?
- 12.A printer starts a job with 480 sheets of paper loaded and prints at a steady rate. The number of sheets left, S, after t minutes is given by S = 480 − 24t. Work out how many minutes it takes for the paper to run out completely.
- 13.Write down the coefficient of xy in the expression 4x²y − 7xy + 2.
- 14.A number machine multiplies its input by 5. Work out the output when the input is −1.
- 15.The first four terms of a sequence are 4, 6, 8, 10. Work out an expression, in terms of n, for the nth term.
Answer key
- (d) 15b — Method: each balloon costs 15p, so b balloons cost 15 × b pence. Working: 15 × b = 15b. Answer: 15b. b + 15 comes from treating the 15p as a one-off addition rather than a rate applied to every balloon. b − 15 comes from misreading the situation as a discount rather than a cost per balloon. b/15 comes from dividing instead of multiplying, swapping the two operations.
- (d) −3 — Substitute y = 11 into y = 5 − 2x, giving 11 = 5 − 2x. Subtracting 5 from both sides gives 6 = −2x, so x = 6 ÷ (−2) = −3. A candidate who mishandles the negative sign when rearranging, treating the equation as 6 = 2x, gets x = 3. A candidate who correctly finds −2x = 6 but forgets to divide by 2 at all gets x = 6. A candidate who adds 5 and 11 instead of subtracting, getting 2x = 16, gets x = 8.
- (b) x = 0 — Method: the first coordinate of a point measures how far to the left or right of the origin it is, so a point that is neither left nor right of the origin has a first coordinate of zero. Working: the y-axis is the vertical line through the origin; every point on it lies directly above or directly below the origin with no sideways movement at all, so its first coordinate is zero while its second coordinate may take any value. Answer: x = 0. The distractors: y = 0 is the condition for lying on the x-axis, the other axis; x = 1 comes from confusing the y-axis with the vertical line one unit to the right of it; x = y is the condition for the diagonal through the origin, which meets the y-axis at the origin only.
- (d) −3 — Method: rewrite the equation in the form y = mx + c, then read off the gradient. Working: y = 4 − 3x can be written as y = −3x + 4, so comparing with y = mx + c gives m = −3. Answer: the gradient is −3. The value 3 comes from ignoring the negative sign on the x term. The value 4 comes from reading off the y-intercept instead of the gradient. The value −4 comes from a sign error, applying the negative sign to the intercept instead of the gradient.
- (a) 7n + 4 — Method: find the common difference, then find the constant that fits the first term. Working: 18 − 11 = 7, 25 − 18 = 7, 32 − 25 = 7, so the terms increase by 7 each time and the nth term has the form 7n + c. Substituting n = 1: 7(1) + c = 11, so c = 4. Answer: the correct nth term is 7n + 4. The value 7n is Ravi's value, which comes from using only the common difference and leaving out the constant. The value 7n + 11 comes from using the first term as the constant directly, without subtracting the common difference first. The value 11n + 7 comes from swapping the roles of the first term and the common difference — using the first term, 11, as the coefficient of n and the difference, 7, as the constant.
- (b) 20 — 3x² − 4x = 3(−2)² − 4(−2) = 3(4) − (−8) = 12 + 8 = 20. A candidate who makes a sign error on −4x, treating −4 × −2 as −8 instead of +8, gets 12 − 8 = 4. A candidate who squares −2 but keeps the result negative, using 3 × (−4) = −12 for the first term, but correctly works out −4x = −4 × (−2) = 8, gets −12 + 8 = −4. A candidate who squares the whole term 3x, working out (3 × −2)² − 4 × (−2), gets (−6)² + 8 = 36 + 8 = 44.
- (c) x = 5 — Method: every point on a vertical line has the same x-coordinate however far up or down the line it lies, so the equation of a vertical line fixes x at a number and does not involve y at all. Working: of the four equations only x = 5 fixes x; it is satisfied by (5, 0), (5, 1), (5, 7) and by every other point whose x-coordinate is 5, and those points form a vertical line. Answer: x = 5. The distractors: y = 5 fixes the y-coordinate instead of the x-coordinate, which gives a horizontal line; y = 5x is a line through the origin with gradient 5, steep but not vertical, and it has a different y-value for every x; x = y fixes neither coordinate and is the line through the origin with gradient 1.
- (b) 3 — Method: a term is any part of an expression separated from the rest by a + or − sign, including a number on its own. Working: 8 − 3x + 5x² splits at the + and − signs into 8, −3x and 5x² — that is three separate terms. Answer: 3. Ryan's answer of 2 comes from wrongly excluding the number 8, thinking a term must contain a letter. 5 comes from miscounting by treating the coefficients and powers as separate terms as well as the letters. 1 comes from treating the whole expression as a single term because it is written without brackets.
- (c) Only x = 5 satisfies 3x + 5 = 20, not every value of x. — 3x + 5 = 20 is only true when x = 5, since 3 × 5 + 5 = 20; for any other value of x the two sides are not equal, so it is an equation, not an identity. Saying it cannot be simplified confuses simplifying with the equation/identity distinction, which is about how many values of x make it true. Saying it has an = sign is not a valid test, since identities are also written with an = or ≡ sign. A number on the right-hand side does not decide it either — what matters is whether both sides match for every value of x, not the form of the right-hand side.
- (b) 6 — 3n + 4.5 = 22.5, so 3n = 18 and n = 6. A candidate who divides 22.5 by 3 first and ignores the 4.5 gets n = 7.5. A candidate who makes a sign error and forms the equation 3n − 4.5 = 22.5 gets 3n = 27 and n = 9. A candidate who divides by 3 before subtracting the 4.5, working out 22.5 ÷ 3 + 4.5, gets n = 12.
- (a) y = (x − 2)² + 3 — Since (x − 2)² is never negative, (x − 2)² + 3 is always at least 3, so y can never equal 0 and the graph never crosses the x-axis. The other three graphs are all given in a factorised or difference-of-squares form that shows two real roots: y = (x − 2)(x + 3) crosses at x = 2 and x = −3; y = x² − 9 = (x − 3)(x + 3) crosses at x = 3 and x = −3; y = (x + 4)(x − 1) crosses at x = −4 and x = 1.
- (a) 20 — Method: the paper has run out when S = 0, so substitute S = 0 into the equation and solve for t. Working: 0 = 480 − 24t, so 24t = 480, and t = 480 / 24 = 20. Answer: it takes 20 minutes. The value 480 comes from giving the starting number of sheets, the intercept of the equation, instead of solving for t. The value 456 comes from working out 480 − 24 and stopping after one step instead of solving the equation fully. The value 0.05 comes from inverting the division, working out 24 / 480 instead of 480 / 24.
- (a) −7 — The coefficient of xy is the number multiplying that exact term, including its sign: in 4x²y − 7xy + 2, the term in xy is −7xy, so the coefficient is −7. Answering 7 correctly picks out the number but drops the minus sign that belongs to it. Answering 4 picks the coefficient of the x²y term instead of the xy term — x²y and xy are different terms because their powers of x differ. Answering −5 combines −7 with the constant term +2, as though the coefficient of xy included the number with no letter attached to it. The coefficient of xy is −7.
- (a) −5 — Method: apply the machine's operation to the input, and carry the sign of the input through the multiplication. Working: the machine gives 5 × (−1); a positive number multiplied by a negative number gives a negative result, and 5 × 1 = 5, so the output is 5 below zero. Answer: −5, which is one lot of −1 taken five times. The distractors: 5 comes from working out 5 × 1 and losing the minus sign of the input; 4 comes from adding 5 to −1 instead of multiplying; −6 comes from subtracting 5 from −1 instead of multiplying.
- (c) 2n + 2 — Method: find the common difference between consecutive terms, then find the constant that fits the first term. Working: 6 − 4 = 2, 8 − 6 = 2, 10 − 8 = 2, so the terms increase by 2 each time and the nth term has the form 2n + c. Substituting n = 1: 2(1) + c = 4, so c = 2. Answer: the nth term is 2n + 2. The value 2n comes from using only the common difference and leaving out the constant c entirely. The value 2n + 4 comes from using the first term itself as c, without subtracting the common difference to find the true constant. The value 2n − 2 comes from a sign error when working out c, giving −2 instead of +2.
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