WAEC Mathematics Past Questions & Answers - Page 131

651.

The sum of 6 and one-third of x is one more than twice x, find x

A.

x = 7

B.

x = 5

C.

x = 3

D.

x = 2

Correct answer is C

6 = \(\frac{1}{3}x\) = 1 + 2x

6 = 1 = \(\frac{2x}{1} - \frac{x}{3}\)

5 = \(\frac{6x - x}{3} = \frac{5x}{3}\)

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

3 x 5 = 5x

15 = 5x

x = \(\frac{15}{5}\)

= 3

652.

Given that P = {x : 1 \(\leq x \leq 6\)}, and Q = {x : 2 \(\leq x \leq 10\)} where x is an integer. Find n(P \(\cap\) Q)

A.

5

B.

6

C.

8

D.

10

Correct answer is A

P = {1, 2, 3, 4, 5, 6}; Q = {3, 4, 5, 6, 7, 8, 9}

P \(\cap\) Q) = {2, 3, 4, 5, 6}

n(P \(\cap\) Q) = 5

653.

A casting is made up of Copper and Zinc. If 65% of the casting is Zinc and there are 147g of Copper. What is the mass of the casting?

A.

320g

B.

420g

C.

520g

D.

620g

Correct answer is B

%Zinc + %Copper = 100%

65% + %Copper = 100%

%Copper = 100% - 65% = 35%

%Copper = \(\frac{\text{Mass of % Copper}}{\text{Mass of Casting}}\) x 100%

Mass of Casting = \(\frac{147}{35}\) x 100%

= 420g

654.

The sum of 2 consecutive whole numbers is \(\frac{5}{6}\) of their product, find the numbers

A.

3, 4

B.

1, 2

C.

2, 3

D.

0, 1

Correct answer is C

Let the no. be x and x + 1

x + (x + 1) = \(\frac{5}{6}\) of x(x + 1)

2x + 1 = \(\frac{5}{6}\) x(x + 1)

6(2x + 1) = 5x2 + 5x

12x + 6 = 5x2 + 5x

5x2 + 5x - 12x - 6 = 0

5x2 - 7x - 6 = 0

5x2 - 10x + 3x - 6 = 0

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

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

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

(5x + 3) = 0

x - 2 = 0

for (5x + 3) = 0

5x = -3

x = \(\frac{-3}{5}\) (Imposible since x is a whole number)

x - 2 = 0

x = 2

x = \(\frac{-3}{5}\)(Impossible since x is a whole number)

x - 2 = 0

x = 2

The numbers are x = 2

x + 1 = 2 + 1

= 3

655.

Simplify 1\(\frac{1}{2} + 2\frac{1}{3} \times \frac{3}{4} - \frac{1}{2}\)

A.

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

B.

-2\(\frac{1}{4}\)

C.

2\(\frac{1}{8}\)

D.

2\(\frac{3}{4}\)

Correct answer is D

1\(\frac{1}{2} + 2\frac{1}{3} \times \frac{3}{4} - \frac{1}{2}\)

\(\frac{3}{2} + \frac{7}{3} \times \frac{3}{4} - \frac{1}{2} = \frac{3}{2} + \frac{7}{4} - \frac{1}{2}\)

= \(\frac{6 + 7 - 2}{4} = \frac{11}{4}\)

= 2\(\frac{3}{4}\)