The radii of two sphere are in the ratio 3 : 2. Their volumes will be in the ratio :

Answer: Option C

Let the radii of the two spheres be 3r and 2r respectively
Then, required ratio :
$$\begin{array}{rl}& =\frac{\frac{4}{3}\pi {\left(3r\right)}^3}{\frac{4}{3}\pi {\left(2r\right)}^3}\\ & =\frac{27}{8}\\ & =27:8\end{array}$$