WAEC Mathematics Past Questions & Answers - Page 85

421.

Find the total surface area of a cylinder of base radius 5cm and length 7cm ( π = 3.14)

A.

17.8cm2

B.

15.8cm2

C.

75.4cm2

D.

54.7cm2

E.

\(377.0cm^{2}\)

Correct answer is E

The total surface area of a cylinder = 2πrl + 2πr2

= 2πr(l + r)

= 2 × 3.14 x 5(7+5)

2 × 3.14 × 12 x 5

= 377.1cm (1DP)

422.

X and Y are two sets such that n(X) = 15, n(Y) = 12 and n{X ∩ Y} = 7. Find ∩{X ∪ Y}

A.

21

B.

225

C.

15

D.

20

Correct answer is D

n(X ∪ Y) = n(X) + n(Y) − n(X ∩ Y) = 15 + 12 − 7 ∴ n(X ∪ Y) = 20

423.

Factorize x2 + 9x + 20

A.

(x − 5) 2

B.

(x + 5)(x + 4)

C.

(x – 5)(x + 3)

D.

(x + 3) 2

Correct answer is B

\( x^2 + 9x + 20 \)

Find the two numbers whose product is 20 and its sum is 9}

\( 5x \times 4x = 20x^2\)


\(5x + 4x = 9x\)

\((x^2 + 5x) + (4x + 20)\)
\(

x(x + 5)+ 4(x + 5)

= (x + 5)(x + 4)\)

424.

Simplify 1¼ ÷ (2 ÷ ¼ of 28)

A.

1 \( \frac{3}{8}\)

B.

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

C.

4 \( \frac{3}{8}\)

D.

3 \( \frac{1}{5}\)

Correct answer is C

1¼ ÷ [ 2 ÷ ¼] of 28

Apply BODMAS rules

\( \frac{5}{4}\) ÷ [ 2 ÷ ¼ × 28 ]

\( \frac{5}{4} ÷ \frac{2}{7} \)


\( \frac{5}{4} × \frac{7}{2} \)

\( \frac{35}{8}\)

= \(4 \frac{3}{8}\)

425.

In the diagram, O is the centre of the circle of the circle, PR is a tangent to the circle at Q < SOQ = 86o. Calculate the value of < SQR.

A.

43o

B.

47o

C.

54o

D.

86o

Correct answer is A

Construction: draw a line from Q to point P and another line from S to point P.

< SOQ = 2< QPS (< at centre is twice < on the circumference)

< QPS \(\frac{86}{2} = 43\)

< SQR = < QPS ( < between a chord and tangent = < in the alternate segment)

< SQR = 43o