WAEC Mathematics Past Questions & Answers - Page 136

676.

Simplify (x - 3y)2 - (x + 3y)2

A.

2(x + 3y)

B.

(2x - 3y)

C.

-12xy

D.

6xy

Correct answer is C

(x - 3y)2 - (x + 3y)2 = [(x - 3y) - (x + 3y)]

[(x + 3y + x + 3y)] = [-6y] [2x]

= -12xy

677.

The angles of triangle are (x + 10)o, (2x - 40)o and (3x - 90)o. Which of the following accurately describes the triangle?

A.

it is a scalene triangle

B.

it is right angled isosceles triangle

C.

it is an equilateral triangle

D.

It is an isosceles triangle but not right angled

Correct answer is C

(x + 10)o + (2x - 40)o + (3x - 90)o = 180

6x - 120 = 180

6x = 180 + 120

6x = 300

x = \(\frac{300}{6}\)

x = 50

x + 10o = 50o + 10o = 60o

2x - 40 = 2(50o) - 40 = 60o

3x - 90 = 3(50o) - 90o = 60o

Hence, it is an equilateral triangle

678.

Simplify; \(\frac{1}{2}\sqrt{32} - \sqrt{18} \sqrt{2}\)

A.

zero

B.

\(\sqrt{2}\)

C.

2\(\sqrt{2}\)

D.

4\(\sqrt{2}\0

Correct answer is A

\(\frac{1}{2}\sqrt{32} - \sqrt{18} \sqrt{2}\) = \(\frac{1}{2} (4\sqrt{2}) - 3\sqrt{2} + \sqrt{2}\)

= 2\(\sqrt{2} - 3\sqrt{2} + \sqrt{2}\)

= 3\(\sqrt{2} - 3\sqrt{2} - 3\sqrt{2}\) = 0

679.

A box contains black, white and red identical balls. The probability of picking a black ball at random from the box is \(\frac{3}{10}\) and the probability of picking a white ball at random is \(\frac{2}{5}\). If there are 30 balls in the box, how many of them are red?

A.

3

B.

7

C.

9

D.

12

Correct answer is C

Total no of balls = 30

Let x = no. of red balls

Pr(red) = \(\frac{x}{30}\)

Pr(black) = \(\frac{3}{10} = \frac{9}{30}\)

Pr(white) = \(\frac{2}{5} = \frac{12}{30}\)

No. of black balls = 9

No. of white balls = 12

9 = 12 + x = 30

x = 30 - 21

x = 9

No. of red balls = 9

680.

A bucket holds 10 litres of water. How many buckets of water will fill a reservoir of size 8m x 7m x 5m.(1 litre = 1000cm3)`

A.

28

B.

280

C.

2800

D.

28000

Correct answer is D

No. of buckets of water = \(\frac{\text{Capacity of reservoir}}{\text{Capacity of buckets}}\)

= \(\frac{800 \times 700 \times 500}{10 \times 1000}\)

= \(\frac{28000 0000}{10000}\)

= 28000