Question 1139265
a volume of circular cylinder is:

{{{V=pi*r^2h}}}

given:
{{{V=320pi*ft^3}}}
{{{h=20ft}}}

{{{320pi*ft^3=pi*r^2*20ft}}}

{{{(320pi*ft^3)/(pi*20ft)=r^2}}}

{{{r^2=16ft^2}}}

{{{r=4ft}}}

=> then diameter of the water tank is: {{{d=2r}}}=>{{{d=8ft}}}

answer: C. 8

Why is it that answer? because, solving equation above, we got radius and diameter is two times greater