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The volume of a cone of height 3cm is 38\(\frac{1}{2}\)cm3. Find the radius of its...

Mathematics
WAEC 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 Answer: Option B
Explanation
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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