The volume of a sphere is [tex]V = \frac{4}{3} \pi r^{3} [/tex], where r is the radius. If the diameter is 10 feet, the radius is 5 feet. Substitute 5 into the volume equation to get [tex]V = \frac{4}{3} \pi 5^{3}[/tex] and use a calculator to solve. The answer rounds to 523.6 cubic feet. Because you are looking for a half full tank, divide 523.6 by 2 to get 261.7 cubic feet.
