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WAEC Mathematics 2018 Paper

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Question : 13

Total: 50

The volume of a cylindrical tank, 10m high is 385 m

^2

. Find the diameter of the tank. [Take

\pi = \frac{22}{7}

]

14m
10m
7m
5m

Solution:

Concept:

The volume of a cylinder is given by

V = \pi r^2 h

, where

r

is the radius and

h

is the height.

Explanation:

Given, volume

V = 385 \, \text{m}^3

and height

h = 10 \, \text{m}

.

Using

\pi = \frac{22}{7}

, we write:

385 = \frac{22}{7} \times r^2 \times 10

385 \times 7 = 22 \times r^2 \times 10

r^2 = \frac{385 \times 7}{22 \times 10}

r^2 = \frac{2695}{220} = 12.25

r = \sqrt{12.25} = 3.5 \, \text{m}

The diameter is twice the radius:

d = 2r = 2 \times 3.5 = 7 \, \text{m}

Answer:

The diameter of the tank is

7 \, \text{m}

, which is option C.

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