Question 206148
The surface area of a sphere is found by {{{SA=4*pi*r^2}}}
Given that the diameter is 20ft, the radius is {{{20/2}}}=10ft
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The surface area is therefore {{{SA=4*pi*10^2}}} = {{{400*pi}}} square feet.
Divide that by 400ft per gallon of paint, and you need {{{pi}}} gallons of paint, which is around 3.14.