PreCalculus
posted by Samantha on .
I'm so confused... I've always been good at math but this year I'm just not getting it. But I know i can I always get help and a REAL explanation from the people on here so...
A steel drum in the shape of a right circular cylinder required to have a volume of 100 cubic feet.
(a) Express the amount A of material required to the make the drum as a function of the radius "r" to the cylinder.
(b) How much material is required if the drum is of radius 3 feet?
(c) Of radius 4 feet?
(d) Of radius 5 feet?
I'm so confused, I don't even know where to start!!!

They want the surface area of the cylinder, including top and bottom. The two ends have a combined area of 2 pi r^2. The side wall area is 2 pi r L, where L is the length. The relationship between L and r is
pi r^2 L = 100
Write the equation for A, using
L = 100/(pi r^2) to eliminate L
Then plug in the numbers. 
Thanks! I didn't realize it could be so easy!