Cylinders

[dddannie6]

I am not sure how to set up this question:

Jake had enough clay to make exactly 6 right circular cylinders, each 8 inches in diameter and 1 inch in height. Using the entire amount of clay, Jake made right circular cylinders that were each 4 inches in diameter and 1 inch in height. How many 4-inch cylinders did he make?

A) 3 B) 9 C) 12 D) 18 E) 24

The answer is 24, I just have no idea how to set this up. Do I use surface area or volume to figure this out?

-Dannialles

[tommywallach]

Hey Dannialles,

So we'll start by using the given information to work out how much clay there is. You have to know the equation for the volume of a cylinder (V = pi * r^2 * height).

V = pi * 4^2 * 1 = 16pi

That's only one cylinder, so we have to multiply by 6: 16pi * 6 =96pi

Now, let's find out how much clay is one of these smaller cylinders: V = pi * 2^2 * 1 = 4pi

Now we can divide to find out how many of these smaller cylinders we could make: 96pi / 4pi = 24

Hope that helps!

-t