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?

let the radius of the pool be Rft

Radius of the pool including the wall = (R+4)ft

Area of the concrete wall = $\pi R+42-R2$= $\pi R+4+RR+4-R = 8\pi R+2$ sq feet

=> 8 $\pi R+2 = \frac{11}{25}\mathrm{\pi R}2 =>11R2 =200R+2$

Radius of the pool R = 20ft