Math CentralQuandaries & Queries


Question from Kristi:

How much oil is in a 40 foot section of pipe that its inside diameter is 36 inches?

Hi Kristi,

The section of pipe is a cylinder. The volume of a cylinder is equal to the area of an end times the length of a cylinder. (The same thing works for long straight boxes with both ends the same size and shape.) The ends of a cylinder are circles, and the area of a circle is pi times the radius squared.

For example, suppose you had a cylinder that was 15 feet long and 6 inches in diameter. To find its volume, first convert the measurements so that they are all in the same units. Since there are 12 inches in a foot, 6 inches = 0.5 feet. The radius is 0.25 feet, so the volume is pi x (0.25)^2 x 15 cubic feet.

If you need the answer is, say, gallons, then you need to figure out how many cubic feet are in a gallon so that you can convert.


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