A circular swimming pool is surrounded by a concrete wall 4ft wide. If the area of the concrete wall surrounding the pool is 11/25 that of the pool, then the radius of the pool is?
Correct Answer: 20ft
let the radius of the pool be Rft
Radius of the pool including the wall = (R+4)ft
Area of the concrete wall = πR+42-R2=πR+4+RR+4-R = 8πR+2 sq feet
=> 8πR+2 = 1125πR2 =>11R2 =200R+2
Radius of the pool R = 20ft