Query Detail : RBI Grade B Phase I

A circular swimming pool is surrounded by a concrete wall 4 ft. 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
Garima,   November 6th 2019,  
RBI Grade B Phase I


Let radius of pool = x ft.

So Area of concrete wall = Pi (x+4)^2 - Pi *x^2 =  11/25* Pi *x^2 

 Pi (x+4)^2  =  11/25* Pi *x^2  + Pi *x^2

Pi{ (x+4)^2}  =  36/25* Pi *x^2 

(x+4)^2 = 36x^2/25 = (6x/5)^2

So x+4 = 6x/5

x/5 = 4

x = 20 ft.

So radius of pool = x = 20 ft.