The circumference of the bas of the cylinder is 18π units. The cylinder is 30 units tall.

Which of the following is the closest to the volume of the cylinder?

A 706 cubic units

B 1,414 cubic units

C 7,630 cubic units

D 21,195 cubic units

The volume of a cylinder is (pi) (radius) ² (height).

We know the height, but we don't know the radius.

Is there a way we can find it?

We know the circumference of the base. Maybe that's a clue.

Can you find the radius of a circle when you know the circumference?

Circumference of a circle = (pi) x (diameter)

18 pi units = (pi) x (diameter)

Divide both sides by pi : 18 units = diameter

Divide both sides by 2 : 9 units = radius yay!

Now we know the radius and the height of the cylinder,

so we can calculate the volume.

radius = 9

height = 30

we'll use 3.14 for pi.

Volume = (pi) (radius) ² (height) =

(3.14) (9) ² (30) =

(3.14) (81) (30) = 7,630.2 cubic units

Is there a choice close to that? I'll go up and look.

Yes! Choice 'C' is 7,630 cubic units. yay!