WAEC Mathematics Past Questions & Answers - Page 145

721.

An arc of a circle, radius 14cm, is 18.33cm long. Calculate to the nearest degree, the angle which the arc subtends at the centre of the circle. [T = \(\frac{22}{7}\)]

A.

11o

B.

20o

C.

22o

D.

75o

Correct answer is D

Length of an arc = \(\frac{\theta}{360} \times 2\pi r\)

18.33 = \(\frac{\theta}{360} \times 2 \times \frac{22}{7} \times 14\)

\(\theta = \frac{18.33 \times 360 \times 17}{2 \times 22 \times 14}\)

= 75o (approx.)

722.

A train travels 60km in M minutes. If its average speed is 400km per hour, find the value of M

A.

15

B.

12

C.

10

D.

9

Correct answer is D

Average speed = \(\frac{Distance}{Time}\)

\(\frac{400km}{hr} = \frac{60km}{Time}\)

Time = \(\frac{60km}{400 km/hr}\)

= \(\frac{60hr}{400}\)

M = \(\frac{60hr}{400} \times \frac{60min}{1hr}\)

= 9 minutes

723.

Simplify \(\frac{\log \sqrt{8}}{\log 4 - \log 2}\)

A.

\(\frac{2}{3}\)

B.

\(\frac{1}{2} \log 2\)

C.

\(\frac{3}{2}\)

D.

\(\log 2\)

Correct answer is C

\(\frac{\log\sqrt{8}}{\log 4 - \log 2} = \frac{\log 8\frac{1}{2}}{\log (\frac{4}{2})}\)

= \(\frac{8 \frac{1}{2}}{\log (\frac{4}{2})}\)

= \(\frac{\frac{1}{2} \log 2^3}{\log 2}\)

= \(\frac{3}{2} \frac{\log 2}{\log 2}\)

= \(\frac{3}{2}\)

724.

If x \(\alpha\) (45 + \(\frac{1}{2}y\)), which of the following is true>?

A.

x varies directly as y

B.

x varies inversely as y

C.

x is partly constant and partly varies as y

D.

x vries jointly as 45 and directly as y

Correct answer is C

No explanation has been provided for this answer.

725.

If \(2^n = 128\), find the value of \(2^{n - 1})(5^{n - 2})\)

A.

5(106)

B.

2(106)

C.

5(105)

D.

2(105)

Correct answer is D

2n = 128

2n = 27

n = 7

(2n - 1)(5n - 2) = (2n - 2.2)(5n - 2) put n = 7

(2n - 1)(5n - 2) = 2(2n - 2 x 5n - 2)

= 2(2 x 5)n - 2

= 2(10n - 2) put n = 7

(2n-1)(5n-2) = 2(105)