# 2013 - WAEC Mathematics Past Questions & Answers - page 1

1
Multiply 2.7 x 10-4 by 6.3 x 106 and leave your answers in standard form
A
1.7 x 103
B
1.70 x 103
C
1.701 x 103
D
17.01 x 103
CORRECT OPTION: c
2.7 x 10-4 x 6.3 x 106

= 2.7 x 6.3 x 10-4 x 106

= 17.01 x 10-4 + 6

= 17.01 x 102

= 1.701 x 101 x 102

= 1.701 x 101 + 2

= 1.701 x 103
2
If 9(2 - x) = 3, find x
A
1
B
$$\frac{3}{2}$$
C
2
D
$$\frac{5}{2}$$
CORRECT OPTION: b
9(2 - x) = 3

32(2 - x) = 3

2(2 - x) = 1

4 - 2x = 1

-2x = 1 - 4

-2x = -3

x = $$\frac{-3}{-2}$$

x = $$\frac{3}{2}$$
3
In what number base is the addition 465 + 24 + 225 = 1050?
A
ten
B
nine
C
eight
D
seven
CORRECT OPTION: d
4
Simplify $$\frac{1\frac{7}{8} \times 2\frac{2}{5}}{6\frac{3}{4} \div \frac{3}{4}}$$
A
9
B
4$$\frac{1}{2}$$
C
2
D
$$\frac{1}{2}$$
CORRECT OPTION: d
$$\frac{1\frac{7}{8} \times 2\frac{2}{5}}{6\frac{3}{4} \div \frac{3}{4}}$$

from numerator $$1 \frac{7}{8} \times 2 \frac{2}{5}$$

= $$\frac{15}{8} \times \frac{12}{5}$$

= $$\frac{3 \times 3}{2 \times 1} = \frac{9}{2}$$

from denominator $$6\frac{3}{4} \div \frac{3}{4}$$

= $$\frac{27}{4} \div \frac{3}{4}$$

= $$\frac{27}{4} \times \frac{4}{3}$$

= $$\frac{9 \times 1}{1 \times 1} = \frac{9}{1}$$

$$\frac{9}{2} \div \frac{9}{1} = \frac{9}{2} \times \frac{1}{9}$$

= $$\frac{1}{2}$$
5
If Un = n(n2 + 1), evaluate U5 - U4
A
18
B
56
C
62
D
80
CORRECT OPTION: c
Un = n(n2 + 1)

U5 = 5(2 + 1)

= 5(25 + 1)

= 5(26) = 130

U4 = 4(42 + 1) = 4(16 + 1)

= 4(17) = 68

U5 - U4 = 130 - 68

= 62
6
If $$\sqrt{50} - K\sqrt{8} = \frac{2}{\sqrt{2}}$$, find K
A
-2
B
-1
C
1
D
2
CORRECT OPTION: d
$$\sqrt{50} - K\sqrt{8} = \frac{2}{\sqrt{2}}$$

$$\sqrt{50} - \frac{2}{\sqrt{2}}$$ = K$$\sqrt{8}$$

= $$\sqrt{2} \times 25 - \frac{2}{\sqrt{2}}$$

= K $$\sqrt{4 \times 2}$$

$$\frac{5\sqrt{2}}{1} - \frac{2}{\sqrt{2}}$$ = 2K$$\sqrt{2}$$

$$\frac{5\sqrt{4} - 2}{\sqrt{2}} = 2K\sqrt{2}$$

$$\frac{10 - 2}{\sqrt{2}} = 2K \sqrt{2}$$

$$\frac{8}{\sqrt{2}} = \frac{2K\sqrt{2}}{1}$$

= 2k$$\sqrt{2} \times \sqrt{2}$$ = 8

2k $$\sqrt{4}$$ = 8

2k x 2 = 8

4k = 8

k = $$\frac{8}{4}$$

k = 2
7
A sales boy gave a change of N68 instead of N72. Calculate his percentage error
A
4%
B
5$$\frac{5}{9}$$%
C
5$$\frac{15}{17}$$%
D
7%
CORRECT OPTION: b
% error = $$\frac{error}{\text{actual value}} \times 100$$

error = N72 - N68 = 4

actual value = N72

%error = $$\frac{4}{72} \times 100$$

= $$\frac{100}{18} = \frac{50}{9}$$ = 5$$\frac{5}{9}$$%
8
Four oranges sell for Nx and three mangoes sell for Ny. Olu bought 24 oranges and 12 mangoes. How much did he pay in terms of x and y?
A
N94x + 6y)
B
N(6x + 4y)
C
N(24x + 12y)
D
N(12x + 24y)
CORRECT OPTION: b
4 oranges sell for Nx, 1 orange will sell for $$\frac{Nx}{4}$$

24 oranges will sell for: $$\frac{Nx}{4} \times 24$$ = n6x

3 mangoes sell for Ny, 1 mango will sell for $$\frac{Ny}{3}$$

12 mangoes will sell for $$\frac{Ny}{3} \times 12$$ = 4Ny

total money pay N6x + N4y = N(6x + 4y)
9
Simplify: $$\frac{x^2 - y^2}{(x + y)^2} + \frac{(x - y)^2}{(3x + 3y)}$$
A
$$\frac{x - y}{3}$$
B
x + y
C
$$\frac{3}{x - y}$$
D
x - y
CORRECT OPTION: c
$$\frac{x^2 - y^2}{(x + y)^2} + \frac{(x - y)^2}{(3x + 3y)}$$

$$\frac{(x + y)(x - y)}{(x + y)(x + y)} + \frac{(x - y)(x - y)}{3(x + y)}$$

= $$\frac{3}{x - y}$$
10
Solve the inequality: $$\frac{2x - 5}{2} < (2 - x)$$
A
x > 0
B
x < $$\frac{1}{4}$$
C
x > 2$$\frac{1}{2}$$
D
x < 2$$\frac{1}{4}$$
CORRECT OPTION: d
$$\frac{2x - 5}{2} < \frac{(2 - x)}{1}$$

2x - 5 < 4 - 2x

2x + 2x < 4 + 5

4x < 9

x < $$\frac{9}{4}$$

x < 2$$\frac{1}{4}$$
Pages: