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WAEC Mathematics Past Questions & Answers - Page 135

671.

Find the quadratic equation whose roots are - $\frac{1}{2}$ and 3

2x² - 2x + 3 = 0

2x² - 2x - 3 = 0

2x² - 5x - 3 = 0

3x² - 5x - 3 = 0

View answer & explanation

Correct answer is C

x = $\frac{-1}{2}$

x = 3

2x = -1, x = 3; 2x + 1 = 0

x - 3 = 0

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

2x2 - 6x + x - 3 = 0

2x2 - 5x - 3 = 0

672.

Simplify (x - 3y)² - (x + 3y)²

2(x + 3y)

(2x - 3y)

-12xy

6xy

View answer & explanation

Correct answer is C

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

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

= -12xy

673.

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

it is a scalene triangle

it is right angled isosceles triangle

it is an equilateral triangle

It is an isosceles triangle but not right angled

View answer & explanation

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 + 10^o = 50^o + 10^o = 60^o

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

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

Hence, it is an equilateral triangle

674.

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

zero

$\sqrt{2}$

2 $\sqrt{2}$

4\(\sqrt{2}\0

View answer & explanation

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

675.

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?

View answer & explanation

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