WAEC Past Questions and Answers - Page 4035

20,171.
20,172.

The density of water is 1g\(cm^3\) while that of ice is 0.9\(cm^3\), calculate the volume change when 90g of ice is completely melted

A.

0\(cm^3\)

B.

9\(cm^3\)

C.

10\(cm^3\)

D.

90\(cm^3\)

E.

100\(cm^3\)

Correct answer is C

V = \(\frac{m}{p} \, ice volume= 90 cm^3;water volume =100 cm^3\\
Volume change = (100-90) cm^3= 10 cm^3\)

20,173.

Solve the equation log8x - 4log8x = 2

A.

1/4

B.

1/2

C.

1

D.

2

E.

4

Correct answer is A

log8x - 4log8x = 2; log8x - log8x4 = 2
log8x/x4 = 2
x/x4 = 82 = 1/x3 = 64
x3 = (1/4)3; x = 1/4

20,174.

Factorise: 6x\(^2\) + 7xy - 5y\(^2\)

A.

(6x + 5y)(x - y)

B.

(2x + 5y)(3x - y)

C.

(3x + y)(2x - 5y)

D.

(3x + 5y)(2x - y)

E.

(2x + y)(3x - 5y)

Correct answer is D

\(6x^2 + 7xy - 5y^2\)

= \(6x^2 + 10xy - 3xy - 5y^2\)

= \(2x(3x + 5y) - y(3x + 5y)\)

= \((2x - y)(3x + 5y)\)

20,175.

Which of the following is a root of the equation x\(^2\) +6x = 0?

A.

0

B.

1

C.

2

D.

3

E.

It does not have any root.

Correct answer is A

\(x^2 + 6x = 0\)

\(x(x + 6) = 0\)

\(x = 0\) or \(x = -6\)