Math CentralQuandaries & Queries


Question from Jim:

Hi, i need to know how many gallons of water can fit into our tank, and how to do the calculations my self. The tank is 72" round by 72" long, i would like some help. Thanks Jim.

Hi Jim,

By '72" round' I assume that the circumference of the circle is 72 inches. The circumference of a circle is given by 2 π r where r is the radius. Thus 2 π r = 72 and hence r = 72/(2 π) = 36/π inches. The volume of a cylinder is given by π r2 h where r is the radius and h is the height. Thus the volume of your tank is

π r2 h = π (36/π)2 × 72 = 29702 cubic inches.

There are 231 cubic inches in an American gallon so the volume of your tank is

29702/231 = 128.58 American gallons.

You can check my arithmetic using our volume calculator.


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