WAEC Past Questions and Answers - Page 2257

11,281.

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

\(∴ 413_7 = 1311_5\)

11,282.

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

11,283.

In the diagram above, M, N, R are points on the circle centre O. ∠ORN = 48° and ∠RNM = 124°. Find ∠OMN.

A.

\(58^0\)

B.

\(64^0\)

C.

\(48^0\)

D.

\(76^0\)

Correct answer is D

Reflex ∠MOR = 2 × 124° = 248° (angle at the centre is twice the angle at the circumference)
∠MOR = 360° - 248° = 112° (sum of angle at a point is 360°)
∠OMN = 360° - (124°+ 48° + 112°) (sum of angles in a quadrilateral is 360°)
= 360° - 284°
∴ ∠OMN = 76°

11,284.

One-third of the sum of two numbers is 12, twice their difference is 12. Find the numbers.

A.

22 and 14

B.

20 and 16

C.

21 and 15

D.

23 and 13

Correct answer is C

Let the two numbers be x and y 

\(\frac{1}{3}( x + y) = 12\)

then x + y = 36 ..........i

2( x - y) = 12

x - y = 6 ............ii

add equations i and ii 

2x = 42

x = 21, put x = 21 into equation i

x + y = 36

21 + y = 36 

y = 36 - 21 = 15

therefore the numbers are 21 and 15

11,285.

The angle of elevation of the top of a building from a point Z on the ground is 50°. If the height of the building is 124 m, find the distance from Z to the foot of the building.

A.

147.78m

B.

104.05m

C.

161.87m

D.

192.91m

Correct answer is B

From the diagram above; Tan\(\theta = \frac{opp}{adj}\)

tan50° = \(\frac{124}{d}\)

d = \(\frac{124}{tan50}\)

therefore, d = 104.05m