A certain rectangular crate measures 20 feet by 20 feet by 20 feet. A cylindrical gas tank is to be made for shipment in the crate and will stand upright when the crate is placed on one of its six faces. What should the radius of the tank be if it is to be of the largest possible volume?
Choose the correct choice from the following options.
A) 4
B) 5
C) 6
D) 8
E) 10

Rationale: "for max volume of cylinder ( pi * r ^ 2 * h ) we need to max out r ^ 2 * h . we do n ' t know what the dimensions of the crate refer to . . therefore for max vol base should be 20 x 20 i . e . of radius 20 / 2 = 10 e"
Answer: E