Question 1
Algebraic ExpressionsIf x + 1/x = 3, find the value of x3 + 1/x3
- A.18
- B.21
- C.27
- D.30
Show the answer and explanation
Answer: A (18)
Cube both sides: x³ + 1/x³ + 3(x + 1/x) = 27, so x³ + 1/x³ = 27 − 3(3) = 18.
24 questions. Try each one, then open the answer to check yourself and read the explanation.
If x + 1/x = 3, find the value of x3 + 1/x3
Answer: A (18)
Cube both sides: x³ + 1/x³ + 3(x + 1/x) = 27, so x³ + 1/x³ = 27 − 3(3) = 18.
Solve for x: log2(x + 1) + log2(x − 2) = 2
Answer: C (3)
(x + 1)(x − 2) = 2² = 4, so x² − x − 6 = 0, giving x = 3 or −2. Logs need x − 2 > 0, so x = 3.
A geometric progression has first term 12 and third term 27. Find the common ratio
Answer: D (±3/2)
ar² = 27 with a = 12, so r² = 27/12 = 9/4 and r = ±3/2 (both signs give third term 27).
If α and β are the roots of the equation 2x2 − 5x + 1 = 0. Find the value of α2 + β2
Answer: C (21/4)
α + β = 5/2 and αβ = 1/2, so α² + β² = (α + β)² − 2αβ = 25/4 − 1 = 21/4.
A line passes through the point (2, −1) and is perpendicular to the line 3x − 2y + 7 = 0. Find its equation
Answer: A (2x + 3y − 1 = 0)
The given line has gradient 3/2, so the perpendicular has gradient −2/3. y + 1 = −2/3(x − 2) gives 3y + 3 = −2x + 4, i.e. 2x + 3y − 1 = 0.
The first 10 terms of an arithmetic progression sum to 185 while the first 5 terms sum to 65. Find the common difference
Answer: C (11/5)
S₅ = 65 gives a + 2d = 13; S₁₀ = 185 gives 2a + 9d = 37. Then 2(13 − 2d) + 9d = 37, so 5d = 11 and d = 11/5.
A bag contains 5 red balls, 4 blue balls and 3 green balls. Two balls are drawn successively without replacement. What is the probability that the two balls are of different colours?
Answer: C (47/66)
P(same colour) = (5×4 + 4×3 + 3×2)/(12×11) = 38/132 = 19/66, so P(different) = 1 − 19/66 = 47/66.
How many 4-digit even numbers can be formed from the digits 1, 2, 3, 4, 5, 6 without repetition?
Answer: D (180)
The last digit must be 2, 4 or 6 (3 ways); the other three places can be filled in 5 × 4 × 3 = 60 ways. Total = 3 × 60 = 180.
The mean of 12 observations is 18. When one observation is recorded as 11 instead of 23, what will the mean be?
Answer: A (17)
The correct total is 12 × 18 = 216. Recording 23 as 11 makes the total 12 less, 204, so the mean becomes 204 ÷ 12 = 17.
A circle has centre O and radius 5cm. From an external point P, a tangent PT is drawn to touch the circle at T. If OP = 13cm, find the length PT
Answer: C (12cm)
The radius OT is perpendicular to the tangent, so PT² = 13² − 5² = 144 and PT = 12 cm.
If tan θ + cot θ = 10/3, where 0° < θ < 90°, find sin 2θ
Answer: C (3/5)
tan θ + cot θ = 1/(sin θ cos θ) = 10/3, so sin θ cos θ = 3/10 and sin 2θ = 2 sin θ cos θ = 3/5.
In a class of 80 students, 42 offer Mathematics, 35 offer Physics and 18 offer both mathematics and physics. How many offer neither?
Answer: A (21)
Number offering at least one = 42 + 35 − 18 = 59, so neither = 80 − 59 = 21.
If the matrix [x 2; 3 x] (first row x, 2; second row 3, x) has a determinant of 16, find x
Answer: C (±√22)
Determinant = x·x − 2·3 = x² − 6 = 16, so x² = 22 and x = ±√22.
If U1 = 2, Un+1 = 2Un + 1, find U4
Answer: C (23)
U₂ = 2(2) + 1 = 5, U₃ = 2(5) + 1 = 11, U₄ = 2(11) + 1 = 23.
If x + y = 10, xy = 21. Find x2y + xy2
Answer: B (210)
x²y + xy² = xy(x + y) = 21 × 10 = 210.
If y varies directly as the square of x and inversely as (x + 1) and x = 2 when y = 8/3, find y when x = 5
Answer: B (25/3)
y = kx²/(x + 1). 8/3 = 4k/3 gives k = 2. When x = 5, y = 2 × 25/6 = 25/3.
Find the coefficient of x3 in the expression (2x − 1/x)5
Answer: B (−80)
The general term is ⁵Cᵣ(2x)⁵⁻ʳ(−1/x)ʳ, with power of x = 5 − 2r. For x³, r = 1: 5 × 2⁴ × (−1) = −80.
If (x + 1)(x + 2)(x + 3) = x3 + ax2 + bx + 6, find the value of a + b.
Answer: C (17)
Expanding gives x³ + 6x² + 11x + 6, so a = 6, b = 11 and a + b = 17.
When the polynomial P(x) = x3 + kx2 − 5x + 7 is divided by (x − 2), the remainder is 9. Find k
Answer: D (1)
By the remainder theorem P(2) = 8 + 4k − 10 + 7 = 9, so 4k = 4 and k = 1.
Find the value of k if the points (1, 2), (3, 5), (k, 8) are collinear
Answer: A (5)
Gradient from (1, 2) to (3, 5) is 3/2; from (3, 5) to (k, 8) it is 3/(k − 3). Equal gradients give k − 3 = 2, so k = 5.
Six students − A, B, C, D, E and F − are to sit around a circular table. In how many distinct arrangements can they sit if A and B must sit next to each other
Answer: A (48)
Treat A and B as one unit: 5 units round a circle give (5 − 1)! = 24 ways, and A and B can swap: 24 × 2 = 48.
Solve 2x+1 + 2x = 48
Answer: D (4)
2ˣ(2 + 1) = 48, so 2ˣ = 16 = 2⁴ and x = 4.
Find the identity element for an operation defined by: a * b = ab − a − b + 2
Answer: C (2)
We need a * e = a: ae − a − e + 2 = a, i.e. (a − 1)(e − 2) = 0 for all a, so e = 2.
A trader marks an item 40% above cost price. He allows a discount of 25%, find his percentage profit or loss
Answer: D (5% profit)
Selling price = 1.4 × 0.75 = 1.05 of cost price, a 5% profit.