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## An empty pool being filled with water at a constant rate

tagged by: Roland2rule

This topic has 4 expert replies and 1 member reply

### Top Member

Roland2rule Legendary Member
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#### An empty pool being filled with water at a constant rate

Thu Mar 01, 2018 12:34 pm
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
OA is B

what is the best mathematical approach to use here? please i need help from expert here
Thanks

### GMAT/MBA Expert

mbawisdom Senior | Next Rank: 100 Posts
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Mon Mar 05, 2018 8:08 am
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
OA is B

what is the best mathematical approach to use here? please i need help from expert here
Thanks
Rate = Work/Time
R = (3/5)/8 = 3/40 pool per hour

We need to fill 2/5 of the pool to finish the job

3/40 = (2/5)/T
3/40 = (16/40)T
T = 16/3 = 5 1/3 hrs or 5 hrs and 20 min

Answer is (B) 5 hr 20 min

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### GMAT/MBA Expert

Scott@TargetTestPrep GMAT Instructor
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Tue Mar 06, 2018 9:23 am
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

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Brent@GMATPrepNow GMAT Instructor
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Mon Mar 05, 2018 8:28 am
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

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Rich.C@EMPOWERgmat.com Elite Legendary Member
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Mon Mar 05, 2018 8:43 pm
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 getâ€¦

8/X = 3/2

Now, cross-multiplyâ€¦

3X = 16

X = 5 1/3 hours

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

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### Top Member

swerve Master | Next Rank: 500 Posts
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Tue Mar 06, 2018 8:13 am
Hi,

As the pool is filled at a constant rate, you can solve it as follow,

8 hours....................................................... 3/5
X hours....................................................... 2/5

Then,
$$X=\frac{8\cdot\frac{2}{5}}{\frac{3}{5}}=\frac{16}{3}=5.33\ hours$$
X = 5 hours and 20 minutes. Option B.

Regards!

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