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WAEC Mathematics Past Questions & Answers - Page 177

881.

A sequence is given by $2\frac{1}{2}, 5, 7\frac{1}{2}, .....$ if the nth term is 25, find n

Correct answer is B

$a = 2\frac{1}{2}, nth = a + (n-1)d \Rightarrow 25 = 2\frac{1}{2} + (n-1)2\frac{1}{2}\\ 25 = \frac{5}{2}+(n-1)\frac{5}{2} \Rightarrow 22\frac{1}{2} = \frac{5n-5}{2}\Rightarrow \frac{45}{2} = \frac{5n-5}{2}\\ 45 = 5n - 5 \Rightarrow 5n = 50 \Rightarrow n = 10$

882.

If $log_9x= 1.5$ ,find x

24.5

13.5

View answer & explanation

Correct answer is B

$log_9x= 1.5\Rightarrow x = 9^{1.5} = 9^{\frac{3}{2}}=(3^2)^{\frac{3}{2}}=3^3=27$

883.

Solve the equation $\frac{2y-1}{3} - \frac{3y-1}{4} = 1$

-8

-13

View answer & explanation

Correct answer is B

$\frac{4(2y-1)-3(3y-1)}{12}=12 \Rightarrow 8y - 4 - 9y + 3 = 12 \\ \Rightarrow -y-1=12\Rightarrow -y=13\Rightarrow y=-13$

884.

Solve the equation 2x - 3y = 22; 3x + 2y = 7

-5

-4

View answer & explanation

Correct answer is B

2x - 3y = 22 ---- eqn I
3x + 2y = 7 ---- eqn II
multiply eqn I by 2
4x - 6y = 44 ---- eqn III
multiply eqn II by 3
9x + 6y = 21 ---- eqn IV
Adding eqn III and IV
=> 13x = 65 => x = 5
Substituting 5 for x in eqn II
3x5 + 2y = 7 => 2y = -8
y = -4

885.

What is the diameter of a circle of area 77cm² [Take $\pi = \frac{22}{7}$ ]

$\frac{\sqrt{2}}{7}cm$

$3\frac{1}{2}cm$

7cm

$7\sqrt{2}cm$

View answer & explanation

Correct answer is D

$A=\pi r^2 \Rightarrow 77 = \frac{22}{7} \times \frac{r^2}{1}\Rightarrow r^2 = \frac{77\times 7}{22} \Rightarrow r^2 = \frac{49}{2}\\ \Rightarrow r = \sqrt{\frac{49}{2}}=\frac{7}{\sqrt{2}}. Since D = 2r ∴ D = 2 \times \frac{7}{\sqrt{2}} = \frac{14}{\sqrt{2}} \times \frac{\sqrt{2}}{\sqrt{2}} = 7\sqrt{2}cm$