Admissions tests / ESAT / Maths 1 / Algebra
Test standard. 15 questions, 15 marks, about 22 minutes.
ESAT Mathematics 1: Algebra, set 1
Algebraic notation and manipulation, expanding and factorising, formulae, linear and quadratic equations, simultaneous equations, inequalities, sequences and graphs.
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- Answer all questions. No calculator.
- Each question has exactly one correct answer.
- 11 mark
Simplify fully: 5(2x - 3) + 4x.
- 21 mark
Simplify fully: (2x^3)^2 / x^4.
- 31 mark
A formula used in mechanics is s = ut + (1/2)at^2, where s is distance, u is initial speed, a is acceleration and t is time. Find s when u = 3, a = 4 and t = 2.
- 41 mark
Expand and simplify (3x - 2)(2x + 5).
- 51 mark
Factorise fully: 2x^2 + 7x + 3.
- 61 mark
Simplify fully: (x^2 - 9) / (x^2 + x - 6).
- 71 mark
Make x the subject of the formula y = (3x + 2)/5.
- 81 mark
For which value of k is 4(x + 3) - 2x = 2x + k true for every value of x?
- 91 mark
A line passes through the points (-2, 5) and (4, -7). Find the equation of the line that is perpendicular to this line and passes through (4, -7).
- 101 mark
By completing the square, find the roots of x^2 - 6x + 5 = 0.
- 111 mark
A quantity of a radioactive substance decreases over time such that it halves every fixed period. Which type of function best models the mass of the substance remaining, m, as a function of time, t?
- 121 mark
A speed-time graph shows an object accelerating uniformly from 0 m/s to 12 m/s over the first 4 seconds, then travelling at a constant 12 m/s for the next 6 seconds. What total distance does the object travel in these 10 seconds?
- 131 mark
Find the two values of x that satisfy the simultaneous equations y = x + 1 and y = x^2 - 5.
- 141 mark
Solve the inequality 5 - 2x >= 1, giving your answer in the form x <= k or x >= k.
- 151 mark
A sequence begins 4, 9, 16, 25, 36, ... Find an expression for the nth term.
Worked solutions
Every question below carries the reasoning, not just the answer. The official material for this test publishes a correct option letter and nothing else.
Question 1Answer: C
- Distribute the 5 across both terms in the bracket: 5(2x - 3) = 5 x 2x - 5 x 3 = 10x - 15.
- Add the remaining 4x term: 10x - 15 + 4x = 14x - 15.
- So 5(2x - 3) + 4x simplifies to 14x - 15, which is option C.
- Why not A: Adds the 4x inside the bracket before distributing, effectively computing 5(2x - 3 + 4x) instead of 5(2x - 3) + 4x.
- Why not B: Makes a sign error when distributing, treating 5 x (-3) as +15 instead of -15.
- Why not D: Distributes the 5 only over the first term inside the bracket (5 x 2x) and forgets to multiply the -3 term by 5 as well.
Question 2Answer: B
- Square everything inside the bracket: (2x^3)^2 = 2^2 x^(3 x 2) = 4x^6.
- Divide by x^4 using the index law x^a / x^b = x^(a-b): 4x^6 / x^4 = 4x^(6-4) = 4x^2.
- So (2x^3)^2 / x^4 simplifies to 4x^2, option B.
- Why not A: Squares the x^3 term correctly to get x^6 but does not square the coefficient 2, carrying it over unchanged as if (2x^3)^2 = 2x^6.
- Why not C: Ignores the coefficient 2 altogether when squaring the bracket, as if (2x^3)^2 = x^6.
- Why not D: Adds the exponents instead of subtracting when dividing by x^4, computing 4x^(6+4) instead of 4x^(6-4).
Question 3Answer: D
- Substitute u = 3, a = 4, t = 2 into s = ut + (1/2)at^2.
- Compute the first term: ut = 3 x 2 = 6.
- Compute the second term: (1/2)at^2 = (1/2) x 4 x 2^2 = (1/2) x 4 x 4 = 8.
- Add the two terms: s = 6 + 8 = 14, so the answer is D.
- Why not A: Omits the 1/2 coefficient on the acceleration term, computing ut + at^2 = 6 + 16 = 22 instead of ut + (1/2)at^2.
- Why not B: Uses t instead of t^2 in the second term, computing ut + (1/2)at = 6 + 4 = 10.
- Why not C: Misreads the formula's structure and combines u with (1/2)a before multiplying by t^2, giving (u + (1/2)a) t^2 = 5 x 4 = 20 with the ut term dropped entirely.
Question 4Answer: A
- Multiply each term in the first bracket by each term in the second: 3x x 2x = 6x^2, 3x x 5 = 15x, -2 x 2x = -4x, -2 x 5 = -10.
- Combine the like (x) terms: 15x - 4x = 11x.
- Add everything together: 6x^2 + 11x - 10, which is option A.
- Why not B: Combines the middle terms 15x and -4x with a sign error, getting -11x instead of +11x.
- Why not C: Treats -4x as +4x when combining middle terms, adding 15x + 4x = 19x instead of 15x - 4x = 11x.
- Why not D: Drops the negative sign on the -2 when multiplying the constant terms, computing 2 x 5 = +10 instead of -2 x 5 = -10.
Question 5Answer: A
- For 2x^2 + 7x + 3, look for factors of the form (2x + p)(x + q) where p and q are factors of 3, the constant term.
- The factor pairs of 3 are 1 and 3. Try (2x + 1)(x + 3): expanding gives 2x^2 + 6x + x + 3 = 2x^2 + 7x + 3, which matches.
- So 2x^2 + 7x + 3 factorises as (2x + 1)(x + 3), option A.
- Why not C: Chooses negative factors of 3 even though both the x-term and constant are positive, writing (2x - 1)(x - 3); expanding this gives 2x^2 - 7x + 3, with the wrong sign on the middle term.
- Why not D: Correctly finds the factor pair (2x + 1)(x + 3) but then drops the leading coefficient 2 from the first bracket, writing (x + 1)(x + 3) instead.
- Why not B: Pairs the factors of 3 with the wrong terms, writing (2x + 3)(x + 1); expanding this gives 2x^2 + 5x + 3, not 2x^2 + 7x + 3.
Question 6Answer: B
- Factorise the numerator: x^2 - 9 is a difference of two squares, so x^2 - 9 = (x - 3)(x + 3).
- Factorise the denominator: x^2 + x - 6 = (x + 3)(x - 2), since 3 x (-2) = -6 and 3 + (-2) = 1.
- Cancel the common factor (x + 3) from the top and bottom: [(x - 3)(x + 3)] / [(x + 3)(x - 2)] = (x - 3)/(x - 2).
- So the fully simplified fraction is (x - 3)/(x - 2), option B.
- Why not A: Factorises the denominator with the signs swapped, as (x - 3)(x + 2) instead of (x + 3)(x - 2), then cancels the resulting common (x - 3) factor, leaving (x + 3)/(x + 2).
- Why not C: Factorises the denominator with a sign error on the second bracket, as (x + 3)(x + 2) instead of (x + 3)(x - 2), then correctly cancels the common (x + 3) factor, leaving (x - 3)/(x + 2).
- Why not D: Cancels the whole denominator (x + 3)(x - 2) against the (x + 3) factor in the numerator, incorrectly treating the entire denominator as a single common factor and leaving just x - 3.
Question 7Answer: B
- Start with y = (3x + 2)/5 and multiply both sides by 5 to clear the fraction: 5y = 3x + 2.
- Subtract 2 from both sides: 5y - 2 = 3x.
- Divide both sides by 3: x = (5y - 2)/3, which is option B.
- Why not C: Makes a sign error rearranging 5y = 3x + 2, adding 2 to both sides instead of subtracting it, giving 3x = 5y + 2.
- Why not D: Divides only the 5y term by 3 and forgets to divide the -2 as well, giving x = 5y/3 - 2 instead of x = (5y - 2)/3.
- Why not A: Forgets to multiply both sides by 5 first, treating y = (3x + 2)/5 as if it were simply y = 3x + 2, giving x = (y - 2)/3.
Question 8Answer: C
- Simplify the left-hand side: 4(x + 3) - 2x = 4x + 12 - 2x = 2x + 12.
- For 2x + 12 = 2x + k to hold for every value of x, this is an identity, so the constant terms must match once the x terms agree.
- So k must equal 12, option C.
- Why not A: Divides the constant term by 2 by mistake, perhaps trying to also halve the constant the way the x-terms combine, giving k = 6 instead of k = 12.
- Why not D: Forgets to combine 4x and -2x into 2x on the left-hand side first, and compares 4x + 12 to 2x + k term by term, doubling the constant to k = 24.
- Why not B: Makes an arithmetic slip expanding the bracket, computing 4 x 3 as 10 instead of 12.
Question 9Answer: A
- Find the gradient of the original line through (-2, 5) and (4, -7): m = (-7 - 5)/(4 - (-2)) = -12/6 = -2.
- A line perpendicular to it has gradient equal to the negative reciprocal: m = -1/(-2) = 1/2.
- Use the point (4, -7) with this gradient in y - y1 = m(x - x1): y - (-7) = (1/2)(x - 4), so y + 7 = (1/2)x - 2.
- Rearranging gives y = (1/2)x - 9, option A.
- Why not B: Uses the original line's gradient of -2 directly instead of finding the negative reciprocal needed for a perpendicular line.
- Why not D: Takes the reciprocal of the original gradient but forgets to flip its sign, using -1/2 instead of the correct perpendicular gradient of 1/2.
- Why not C: Uses the correct perpendicular gradient of 1/2 but fails to multiply the 4 inside the bracket by 1/2, keeping it as -4 instead of -2.
Question 10Answer: D
- Complete the square: x^2 - 6x + 5 = (x - 3)^2 - 9 + 5 = (x - 3)^2 - 4.
- Set the expression equal to zero: (x - 3)^2 - 4 = 0, so (x - 3)^2 = 4.
- Take the square root of both sides: x - 3 = 2 or x - 3 = -2.
- Solve each case: x = 5 or x = 1, so the roots are x = 1 and x = 5, option D.
- Why not A: Forgets to take the square root of 4 when solving (x - 3)^2 = 4, and instead sets x - 3 equal to 4 or -4 directly, giving x = 7 or x = -1.
- Why not B: Forgets to subtract 9 when completing the square, incorrectly writing x^2 - 6x + 5 as (x - 3)^2 + 5, which gives (x - 3)^2 = -5 and wrongly concludes there are no real roots.
- Why not C: Writes the completed square form with the wrong sign inside the bracket, as (x + 3)^2 - 4 instead of (x - 3)^2 - 4, and so solves x + 3 = 2 or x + 3 = -2 to get x = -1 or x = -5.
Question 11Answer: A
- Halving over equal fixed periods means the mass is multiplied by the same factor, 1/2, each period, not reduced by the same fixed amount.
- A quantity that is repeatedly multiplied by a constant factor over equal time intervals is modelled by an exponential function, m = m0 x k^t, where here k = 1/2.
- So the correct model is an exponential function, option A.
- Why not C: Mistakes 'the mass keeps halving' for inverse proportion between mass and time, which would make the mass fall in a different pattern to repeated halving over equal time periods.
- Why not D: Mistakes the shape of a decaying exponential curve for part of a downward parabola, which would mean the rate of decrease keeps changing in a way that does not match repeated halving over equal time periods.
- Why not B: Models the decrease as happening at a constant rate (a straight line), which would mean the mass drops by the same fixed amount each period rather than by the same fixed fraction.
Question 12Answer: D
- During the first 4 seconds the object accelerates uniformly from 0 to 12 m/s, so this section of the graph is a triangle with area (1/2) x 4 x 12 = 24 m.
- During the next 6 seconds the speed is constant at 12 m/s, so this section is a rectangle with area 6 x 12 = 72 m.
- The total distance is the sum of the two areas: 24 + 72 = 96 m, option D.
- Why not A: Only calculates the area of the constant-speed rectangle (6 s x 12 m/s = 72 m) and forgets to include the distance covered during the first 4 seconds of acceleration.
- Why not B: Treats the whole 10 seconds as if the object travelled at the constant final speed of 12 m/s throughout, computing 10 x 12 = 120 m, which ignores that the object started from rest.
- Why not C: Applies the average speed of the first phase (6 m/s, halfway between 0 and 12) to the entire 10 second interval, computing 6 x 10 = 60 m, instead of only to the first 4 seconds.
Question 13Answer: C
- Set the two expressions for y equal to each other: x + 1 = x^2 - 5.
- Rearrange so everything is on one side: 0 = x^2 - x - 6, i.e. x^2 - x - 6 = 0.
- Factorise: we need two numbers that multiply to -6 and add to -1, which are -3 and 2, so x^2 - x - 6 = (x - 3)(x + 2).
- Setting each factor to zero gives x = 3 or x = -2, option C.
- Why not B: Picks a factor pair of -6 (namely 6 and -1) that gives the right product but does not check that the pair also sums to -1, the coefficient of x; 6 and -1 sum to 5, not -1.
- Why not D: Picks the factor pair -6 and 1, which also gives the right product but sums to -5, not -1, so does not actually satisfy the equation.
- Why not A: Rearranges x + 1 = x^2 - 5 with a sign error on the linear term, getting x^2 + x - 6 = 0 instead of x^2 - x - 6 = 0, which factorises as (x + 3)(x - 2) giving x = -3 or x = 2.
Question 14Answer: A
- Start with 5 - 2x >= 1 and subtract 5 from both sides: -2x >= 1 - 5, so -2x >= -4.
- Divide both sides by -2. Dividing an inequality by a negative number reverses its direction, so x <= 2.
- The solution is x <= 2, option A.
- Why not C: Divides both sides by -2 correctly in every other respect but forgets to reverse the inequality sign when dividing by a negative number, giving x >= 2 instead of x <= 2.
- Why not D: Makes a sign error moving the 5 across the inequality, computing -2x >= 1 + 5 = 6 instead of -2x >= 1 - 5 = -4, though the inequality is correctly reversed when dividing by -2.
- Why not B: Combines both errors: moves the 5 with the wrong sign (getting -2x >= 6) and then also forgets to reverse the inequality sign when dividing by -2, giving x >= -3.
Question 15Answer: D
- Find the first differences of 4, 9, 16, 25, 36: 5, 7, 9, 11.
- Find the second differences of those: 2, 2, 2, which is constant, confirming this is a quadratic sequence with n^2 coefficient equal to half the second difference, so a = 2/2 = 1.
- Subtract n^2 from each term to find what remains: 4 - 1 = 3, 9 - 4 = 5, 16 - 9 = 7, 25 - 16 = 9, 36 - 25 = 11, which is the linear sequence 3, 5, 7, 9, 11 with nth term 2n + 1.
- Combine the two parts: the nth term of the original sequence is n^2 + 2n + 1, option D.
- Why not A: Correctly finds the n^2 coefficient and the linear coefficient but forgets to include the constant term, giving n^2 + 2n instead of n^2 + 2n + 1.
- Why not C: Uses the sequence's first term and first common difference directly as the constant and linear coefficients, without first subtracting n^2 from each term to find the remaining linear sequence.
- Why not B: Uses the full second difference (2) as the coefficient of n^2 instead of half of it, forgetting that the coefficient of n^2 in a quadratic sequence is always half the constant second difference, while still keeping the correctly found linear part 2n + 1 unchanged, giving 2n^2 + 2n + 1.
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