Problem:
Which cylinder has twice the volume of the cylinder shown below?
Answer Choices:
A. 
B. 
C. 
D. 
E. None of the above
Solution:
Cylinder can be obtained by stacking one copy of the given cylinder on top of another. The formula for the volume of a cylinder with radius and height is . Use this to show that none of the other cylinders has twice the volume of the given cylinder:
Note. If the radius remains the same and the height is doubled, then the volume will double, as in . Doubling the radius while the height remains the same will multiply the volume by , as in .
Answer: .
The problems on this page are the property of the MAA's American Mathematics Competitions