WAEC Mathematics Past Questions & Answers - Page 225

1,121.

If x varies inversely as y and \(x = \frac{2}{3}\) when y = 9, find the value of y when \(x=\frac{3}{4}\)

A.

\(\frac{1}{18}\)

B.

\(\frac{8}{81}\)

C.

\(\frac{9}{2}\)

D.

8

Correct answer is D

\(x \propto \frac{1}{y}\)

\(x = \frac{k}{y}\)

\(\frac{2}{3} = \frac{k}{9}\)

\(3k = 18 \implies k = 6\)

\(x = \frac{6}{y}\)

When y = \(\frac{3}{4}\),

x = \(\frac{6}{\frac{3}{4}}\)

= \(\frac{6 \times 4}{3}\)

= 8

1,122.

Given that \(27^{(1+x)}=9\) find x

A.

-3

B.

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

C.

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

D.

2

Correct answer is B

\(27^{(1+x)}=9\\
3^{3(1+x)}=3^2\\
3(1+x)=2\\
3+3x = 2\\
3x = -1
x = \frac{-1}{3}\)

1,123.

Given that \(x = -\frac{1}{2}and \hspace{1mm} y = 4 \hspace{1mm} evaluate \hspace{1mm} 3x^2y+xy^2\)

A.

-5

B.

-1

C.

4

D.

11

Correct answer is A

\(x = -\frac{1}{2}, y = 4\\
3x^2y + xy^2\\
3\left[-\frac{1}{2}\right]^2 \times 4 \times + \left(\frac{-1}{2}\right)(4)^2\\
3\times \frac{1}{4} \times 4 -\frac{1}{2} \times 16\\
3-8 = -5\)

1,124.

In the diagram, POS and ROT are straight lines, OPQR is a parallelogram. |OS| = |OT| and ∠OST = 50°. Calculate ∠OPQ.

A.

160o

B.

140o

C.

120o

D.

100o

Correct answer is D

< T = < S = 50° (OS = OT)

< SOT = 180° - 2(50°) = 80°

< ROP = 80° (vertically opposite angle)

\(\therefore\) < OPQ = 180° - 80° = 100° (adjacent angles)

1,125.

If the interior angles of hexagon are 107°, 2x°, 150°, 95°, (2x-15)° and 123°, find x.

A.

\(57\frac{1}{2}^{\circ}\)

B.

\(65^{\circ}\)

C.

\(106^{\circ}\)

D.

\(120^{\circ}\)

Correct answer is B

Sum of interior angle in a hexagon = (6 - 2) x 180°

= 720°

\(\therefore\) 107° + 2x° + 150° + 95° + (2x - 15)° + 123° = 720°

460 + 4x = 720 \(\implies\) 4x = 720 - 460

4x = 260° \(\implies\) x = 65°