Problem:
Which of the cones below can be formed from a sector of a circle of radius by aligning the two straight sides?
Answer Choices:
A. .jpg)
B. 
C. 
D. .jpg)
E. 
Solution:
The slant height of the cone is , the radius of the sector. The circmference of the base of the cone is the same as the length of the secotr's arc. This is of the circumference, , of the circle from which the sector is cut. The base circumference of the cone is , so its radius is .
Answer: .
The problems on this page are the property of the MAA's American Mathematics Competitions