Question:
If the height and the radius of a cone are doubled, the volume of the cone becomes
(a) 3 times
(b) 4 times
(c) 6 times
(d) 8 times
Solution:
(d) 8 times
Let the new height and radius be 2h and 2r, respectively.
New volume of the cone $=\frac{1}{3} \pi(2 r)^{2} \times 2 h$
$=\frac{8}{3} \pi r^{2} h=8 \times$ initial volume of the cone