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

[Gmat_mission]

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

[spoiler]OA=B[/spoiler]

Source: Official Guide

[JamesHammel]

X = 3/5 = 8 hours

Y = 2/5 = remaining time needed

\(\frac{Y}{8}=\frac{\frac{2}{5}}{\frac{3}{5}}\)

\(\frac{Y}{8}=\frac{2}{3}\)

3Y = 16

Y = 16/3 = 5.333

1/3 of an hour is 20 mins

=> The time required to fill the rest of the pool (Y) will be 5 hours 20 minutes (B)

[Scott@TargetTestPrep]

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

[spoiler]OA=B[/spoiler]

Source: Official Guide

Solution:

We need to find the time to fill the remaining 2/5 of the pool. Thus, we can use the following proportion:

8/(3/5) = x/(2/5)

40/3 = 5x/2

15x = 80

x = 80/15 = 16/3 = 5 ⅓ hr = 5 hr 20 min

Alternate Solution:

Let's assume the capacity of the pool is 5 gallons. Since it takes 8 hours to fill 3/5 x 5 = 3 gallons, the pool is filled at a rate of 3/8 gallons per hour. Since 3 gallons of the pool is already filled, the remaining 5 - 3 = 2 gallons will be filled in 2 x (8/3) = 16/3 = 5 1/3 hours; or 5 hours and 20 minutes.

Answer: B