Q186
ArithmeticGeometry & Mensuration
A circular swimming pool is surrounded by a concrete wall 4 ft wide. If the area of the concrete wall surrounding the pool is $\frac{11}{25}$ that of the pool, then the radius of the pool is
- a.8 ft
- b.16 ft
- c.20 ft
- d.30 ft
Answer: (C) 20 ft
Pool plus wall has area $\frac{36}{25}$ of the pool, so the outer radius is $\frac{6}{5}$ of the pool radius R. Then R + 4 = $\frac{6R}{5}$, giving R = 20 ft. With R = 16 ft the wall's share would be about 0·56 of the pool.