An empty pool being filled with water at a constant rate takes 8 hours

An empty pool being filled with water at a constant rate takes 8 hours to fill to 3/5 of its capacity. How much more time will it take to finish filling the pool?

(A) 5 hr 30 min
(B) 5 hr 20 min
(C) 4 hr 48 min
(D) 3 hr 12 min
(E) 2 hr 40 min


As pool is filled to 3/5 of its capacity then 2/5 of its capacity is left to fill.

Since it takes 8 hours to fill 3/5 of the pool, then to fill 2/5 of the pool it will take \(\frac{8}{(\frac{3}{5})}*\frac{2}{5} = \frac{16}{3} \ hours = 5 \ hours \ 20 \ minutes\) (because if t is the time needed to fill the pool then \(t*\frac{3}{5}=8\) --> \(t=8*\frac{5}{3} \ hours\) --> to fill 2/5 of the pool \(8*\frac{5}{3}*\frac{2}{5}=\frac{16}{3}\) hours will be needed).

Or plug values: take the capacity of the pool to be 5 liters --> 3/5 of the pool or 3 liters is filled in 8 hours, which gives the rate of 3/8 liters per hour --> remaining 2 liters will require: \(time = \frac{job}{rate} = \frac{2}{(\frac{3}{8})} = \frac{16}{3} \ hours = 5 \ hours \ 20 \ minutes\).

Answer: B.