Question on: WAEC Mathematics - 2015
The volume of a cone of height 3cm is 38(\frac{1}{2})cm3. Find the radius of its base. [Take (\pi = \frac{22}{7})]
A
3.0cm
B
3.5cm
C
4.0cm
D
4.5cm
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Correct Option: B
Using V = (\frac{3}{1} \pi r^2h),
so, 38(\frac{1}{2} = \frac{1}{3} \times \frac{22}{7} \times r^2 \times 3)
(\frac{77}{2} = \frac{22}{7} \times r^2)
r2 = (\frac{77 \times 7}{2 \times 22})
r2 = (\frac{49}{4})
Hence, r = (\sqrt{\frac{49}{4}})
= 3(\frac{1}{2})
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