How long should the radius of the pool be?

Question

Joe wants to build a circular pool in his backyard. The rectangular backyard measures 40 feet wide by 70 feet long. Joe wants the pool to be as large as possible, with the edge of the pool at least 4 feet from the edge of the backyard all around. How long should the radius of the pool be in feet?

Answer 1

The diameter is limited to 40 ft, less 4 ft at each end, so diameter (max.) is 32.  Therefore the radius maximum is 16 ft.