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?  Pick one:	A) 10ft	B) 20ft	C) 30ft	D) 40ft	E) 50ft
Explanation:   let the radius of the pool be Rft   radius of the pool including the wall = (R+4)ft   area of the concrete wall = π[(R + 4)2 - R2] = π[(R + 4 + R)(R + 4 - R)] = 8π(R + 2) sq feet   ⇒ 8π(R + 2) = 11/25πR2 ⇒ 11 R2 = 200(R + 2)   Radius of the pool R = 20ft Answer: 20ft
<result>B</result>
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?