An empty pool being filled with water at a constant rate

Roland2rule wrote: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

Here's another approach:

IMPORTANT CONCEPT: After 8 hours, 3/5 of the job is finished and 2/5 of the job is remaining.
This means the remaining part of the job is 2/3 the size of the first part of the job.
Think of it this way:
If the pool had a capacity of 5 gallons, then the first part of the job would be filling 3 gallons, and the remaining part of the job is filling 2 gallons.
So, the remaining part of the job (filling 2 gallons) is 2/3 the size of the first part of the job (filling 3 gallons)

So, if it takes 8 hours to do the first part of the job, the time to do the remaining part = 2/3 of 8 hours
2/3 of 8 hours = 2/3 x 8 hours
= 16/3 hours
= 5 1/3 hours
= 5 hours 20 minutes

Answer: B

Hi Roland2rule,

We're told that 8 hours fills 3/5 of the pool; the question asks how long it will take to fill the remaining 2/5 of the pool. Since the pool is filling at a constant rate, we can use a ratio to answer the question. The ratio can be written in a number of different ways; I used the following ratio:

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

Simplifying, we get…

8/X = 3/2

Now, cross-multiply…

3X = 16

X = 5 1/3 hours

Final Answer: B

GMAT assassins aren't born, they're made,
Rich

Roland2rule wrote: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

We can let n = the time it takes to fill the remaining 2/5 of the pool and create the proportion:

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

40/3 = 5n/2

80 = 15n

n = 80/15 = 16/3 = 5 1/3 hours = 5 hours and 20 minutes

Answer: B