WAEC Mathematics Past Questions & Answers - Page 205

1,021.

A number is selected at random from the set Y = {18, 19, 20, . . . 28, 29}. Find the probability that the number is prime.

A.

\(\frac{1}{4}\)

B.

\(\frac{3}{11}\)

C.

\(\frac{1}{2}\)

D.

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

Correct answer is A

Y = {18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29}

Number of prime numbers = 3

Prob(picking  a prime number) = \(\frac{3}{12}\)

= \(\frac{1}{4}\)

1,022.

The base diameter of a cone is 14cm, and its volume is 462 cm3. Find its height. [Taken \(\pi = \frac{22}{7}\)]

A.

3.5cm

B.

5cm

C.

7cm

D.

9cm

Correct answer is D

From \(V = \frac{1}{3}\pi r^2 h. \hspace{1mm} r =\frac{14}{2}\\
462 = \frac{1}{3} \times \frac{22}{7} \times 7^2 \times h \\
h = \frac{3 \times 462}{22 \times 7}\\ h = 9\)

1,023.

The lengths of the parallel sides of a trapezium are 9 cm and 12 cm. lf the area of the trapezium is 105 cm2, find the perpendicular distance between the parallel sides.

A.

5cm

B.

7cm

C.

10cm

D.

15cm

Correct answer is C

\(\frac{1}{2}(a+b)\times h = 105cm^2\\
\frac{1}{2}(9+12)\times h = 105\\
h = \frac{105 \times 2}{21} = 10cm\)

1,024.

Simplify \(\frac{1}{1-x} + \frac{2}{1+x}\)

A.

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

B.

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

C.

\(\frac{3-x}{1-x^2}\)

D.

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

Correct answer is C

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

1,025.

For what values of x is the expression \(\frac{3x-2}{4x^2+9x-9}\) undefined?

A.

\(\frac{-3}{4} \hspace{1mm}or \hspace{1mm}3\)

B.

\(\frac{-2}{3} \hspace{1mm}or \hspace{1mm}-3\)

C.

\(\frac{2}{3} \hspace{1mm}or \hspace{1mm}3\)

D.

\(\frac{3}{4} \hspace{1mm}or \hspace{1mm}-3\)

Correct answer is D

The equation \(\frac{3x - 2}{4x^2 + 9x - 9}\) is undefined when the denominator = 0.

\(4x^2 + 9x - 9 = 0\)

\(4x^2 + 12x - 3x - 9 = 0\)

\(4x(x + 3) - 3(x + 3) = 0\)

\((4x - 3)(x + 3) = 0\)

x = \(\frac{3}{4}\) or x = -3.