Geometry
posted by Samantha on .
Two cylinders have the same volume. If the radius of cylinder I is 3 times the radius of cylinder II, then the height of cylinder II is how many times the height of cylinder I?
A. 12
B. 9
C. 6
D. 3
Please explain how, if possible.

Cylinder 1 has nine times the base area of cylinder 2.
Volume is (base area) x (height)
For the volumes to be equal, cylinder 2 must have 9 times the height of cylinder 2. 
pi*r^2*h2 = pi*(3r)^2*h1.
pi*r^2*h2 = pi*9r^2*h1
Divide both sides by pi*r^2:
h2 = 9*h1. 
For the volumes to be equal, cylinder 2 must have 9 times the height of cylinder 1