WAEC Mathematics Past Questions & Answers - Page 92

456.

A chord, 7cm long, is drawn in a circle with radius 3.7cm. Calculate the distance of the chord from the centre of the circle

A.

0.7cm

B.

1.2cm

C.

2.0cm

D.

2.5cm

Correct answer is B

let the chord be AB = 7cm

radius OA = 3.7cm distance of the = OM using Pythagoras theorem

OA2 = AM2 + OM2

3.72 = 3.52 + OM2

13.69 = 12.25 + OM2

13.69 - 12.25 = OM2

1.44 = OM2

OM = \(\sqrt{1.44}\)

OM = 1.2cm

distance of chord = 1.2cm

457.

The area of a sector a circle with diameter 12cm is 66cm2. If the sector is folded to form a cone, calculate the radius of the base of the cone [Take \(\pi = \frac{22}{7}\)]

A.

3.0cm

B.

3.5cm

C.

7.0cm

D.

7.5cm

Correct answer is B

diameter = 12cm

radius = \(\frac{12}{2}\)cm = 6cm

area of sector = 66cm2

area of sector = area of cone

66 = \(\pi rl\)

66 = \(\frac{22}{7} \times r \times 6\)

divide both sides by 6

11 = \(\frac{22}{7}r\)

22r = 11 x 7

r = \(\frac{77}{22}\)

= 3.5cm

458.

\(\begin{array}{c|c}height & 2 & 3 & 4 & 5 & 6 \\ \hline frequency & 2 & 4 & 5 & 3 & 1
\end{array}\)
The table shows the distribution of the height of plants in a nursery. Calculate the mean height of the plants.

A.

3.8

B.

3.0

C.

2.8

D.

2.3

Correct answer is A

\(\begin{array}{c|c} height(x) & frequency(f) & fx \\ \hline 2 & 2 & 4\\ 3 & 4 & 12\\ 4 & 5 & 20 \\ 5 & 3 & 15\\ 6 & 1 & 6\end{array}\)

mean\(\bar{x} = \frac{\sum fx}{\sum f}\)

= \(\frac{57}{15}\)

= 3.8

459.

If (x - a) is a factor pf bx - ax + x2, find the other factor.

A.

(x + b)

B.

(x - b)

C.

(a + b)

D.

(a - b)

Correct answer is A

No explanation has been provided for this answer.

460.

Find the gradient of the line joining the points (2, -3) and 2, 5)

A.

9

B.

1

C.

2

D.

undefined

Correct answer is D

(2, -3)(2, 5)

gradient = \(\frac{y_ = y_1}{x_2 = x_1} = \frac{5 - (-3)}{2 - 2}\)

= \(\frac{5 + 3}{0}\)

= \(\frac{8}{0}\)

= undefined