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WAEC Mathematics 2018 Paper

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Question : 21

Total: 50

The total surface area of a hemispher is 75

\pi \mathrm{cm}^2

. Find the radius.

5.0 cm
7.0 cm
8.5 cm
12.0 cm

Solution:

Total surface area of hemisphere is

3 $\pi r^2$ = 75 $\pi \mathrm{cm}^2$

$r^2$ = $\;\frac{75\;\pi}{3\;\pi}$

$r^2$ = 25

r = $\sqrt{25}$

r = 5cm

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