A right circular cone has a volume of $24 \pi$ cubic inches. If the height of the cone is 2 inches, what is the radius, in inches, of the base of the cone?
SAT · Math · previous-year question
- A.$2 \sqrt{3}$
- B.6correct
- C.12
- D.36
Answer
B. 6
Explanation
Choice B is correct. The formula for the volume $V$ of a right circular cone is $V=\frac{1}{3} \pi r^{2} h$, where $r$ is the radius of the base and $h$ is the height of the cone. It's given that the cone's volume is $24 \pi$ cubic inches and its height is 2 inches. Substituting $24 \pi$ for $V$ and 2 for $h$ yields $24 \pi=\frac{1}{3} \pi r^{2}(2)$. Rewriting the right-hand side of this equation yields $24 \pi=\left(\frac{2 \pi}{3}\right) r^{2}$, which is equivalent to $36=r^{2}$. Taking the square root of both sides of this equation gives $r= \pm 6$. Since the radius is a measure of length,
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