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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

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 - R 2 = π R + 4 + R R + 4 - R   =   8 π R + 2  sq feet


 


=> 8 π R + 2   =   11 25 πR 2   = > 11 R 2   = 200 R + 2


 


Radius of the pool R = 20ft


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