WAEC Mathematics Past Questions & Answers - Page 19

91.

A weaver bought a bundle of grass for $ 50.00 from which he made 8 mats. If each mat was sold for $ 15.00, find the percentage profit.

A.

240%

B.

140%

C.

120%

D.

40%

Correct answer is B

cost price = $50

Selling price = 15 * 8 = $120

percentage profit = \(\frac{sp-cp}{cp}\) * 100 →  \(\frac{120-50}{50}\) * 100

percentage profit = 70 * 2 → 140%

92.

If 4\(^{3x}\) = 16\(^{x+1}\), find the value of x 

A.

2

B.

3

C.

4

D.

5

Correct answer is A

4\(^{3x}\) = 4\(^{2(x+1)}\)

3x = 2x + 2

3x - 2x = 2

x = 2

93.

Evaluate 23 x 54 (mod 7)

A.

2

B.

3

C.

5

D.

6

Correct answer is B

23 x 54 = 1242

In mod 7; 

1242 ÷ 7 = 177 R 3 

Hence; 1242 ≡ 3

94.

Given that A and B are sets such that n(A) = 8, n(B)=12 and n(AnB) =3, find n(AuB).

A.

15

B.

17

C.

20

D.

23

Correct answer is B

n(AuB) = n(A) + n(B) -  n(AnB)

n(AuB) = 8 + 12 - 3

= 17 

95.

Change 432\(_{five}\)  to a number in base three.

A.

10100\(_{three}\)

B.

11100\(_{three}\)

C.

11101\(_{three}\)

D.

10110\(_{three}\)

Correct answer is B

Convert from base 5 to base 10

432\(_{five}\) =  (4 x 5\(^2\)) + (3 x 5\(^1\)) + (2 x 5\(^0\))

= (4 x 25) + (3 x 5) + (2 x 1)

= 100 + 15 + 2

= 117\(_{ten}\)

Then convert from base 10 to base 3

3 117
3 39 r 0
3 13 r 0
3 4 r 1
3 1 r 1
  0 r 1

Selecting the remainders from bottom to top:

117\(_{ten}\) = 11100\(_{three}\)

Hence; 432\(_{five}\) =  11100\(_{three}\)