WAEC Mathematics Past Questions & Answers - Page 8

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36.

Solve \(2^{5x} \div 2^x = \sqrt[5]{2^{10}}\)

A.

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

B.

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

C.

\(\frac{1}{3}\)

D.

\(\frac{5}{3}\)

Correct answer is B

\(2^{5x} \div 2^x = \sqrt[5]{2^{10}}\)

applying the laws of indices

\(2^{5x - x} = 2^{10(1/5)}\)

\(2^{4x} = 2^{10(1/5)}\)

\(2^{4x} = 2^2\)
Equating the powers
then 4x = 2

therefore, x = \(\frac{2}{4}\) = \(\frac{1}{2}\) 

37.

The interior angle of a regular polygon is 6 times its exterior angle find the number of sides of the polygon.

A.

12

B.

15

C.

10

D.

14

Correct answer is D

each interior angle of a polygon = \(\frac{(n - 2)\times 180}{n}\) where n = no of side of a polygon

each exterior angle of a polygon = \(\frac{360}{n}\)

then  \(\frac{(n - 2)\times 180}{n}\) = 6\(\times\) \(\frac{360}{n}\)

= (n - 2) 180 = 2160

= 180n - 360 = 2160

= 180n = 2160 + 360

= 180n = 2520

therefore, n = \(\frac{2520}{180}\) = 14.

38.

Evaluate, correct to three decimal place \(\frac{4.314 × 0.000056}{0.0067}\)

A.

0.037

B.

0.004

C.

0.361

D.

0.036

Correct answer is D

\(\frac{4.314 × 0.000056}{0.0067}\)

\(\frac{0.000242}{0.0067}\)

= 0.036 ( to 3 decimal places)

39.

Express \(413_7\) to base 5

A.

\(2311_5\)

B.

\(1131_5\)

C.

\(1311_5\)

D.

\(2132_5\)

Correct answer is C

\(413_7\) to base 5 

convert first to base 10

\(417_7 = 4 × 7^2 + 1 × 7^1 + 3 × 7^0\)
= 4 × 49 + 1 × 7 + 3 × 1
= 196 + 7 + 3

= \(206_{10}\)

convert this result to base 5

5 206
5 41R1
5 8R1
5 1R3
  0R1

\(∴ 413_7 = 1311_5\)

40.

For what value of x is  \(\frac{ x^2 + 2 }{ 10x^2 - 13x - 3}\)  is undefined?

A.

\(\frac{1}{5}, \frac{3}{2}\)

B.

\(\frac{-1}{5}, \frac{3}{2}\)

C.

\(\frac{1}{5}, \frac{-3}{2}\)

D.

\(\frac{-1}{5}, \frac{-3}{2}\)

Correct answer is B

The fraction  \(\frac{ x^2 + 2 }{ 10x^2 - 13x - 3}\)  is undefined when the denominator is equal to zero

\(then  10x^2 - 13x - 3 = 0\)

by factorisation,  \(10x^2 - 13x - 3\) = 0 becomes \( 10x^2 - 15x +2x -3\) = 0

\(5x(2x - 3) + 1(2x - 3) = 0\)

\((5x + 1)(2x - 3) = 0\)

\(then, x = \frac{-1}{5}\) or \(\frac{3}{2}\)