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

Question

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

Bunuel · Accepted Answer

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.

sudhir18n · Answer

Its B
I would use percentages to do this ... easy for me

3/5 work = 60% = is done in 8 hrs
remaining will be 40%( percentages are always 100) be done in 8*40/60 = 16/3 = 5 1/3 hrs = 5+1/3*60 = 5.20 hrs

PS:Edited for a typo

BrentGMATPrepNow · Answer

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, then 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

Cheers,
Brent

puneetj · Answer

1st convert to mins to avoid the confusion

60% = 480 mins
therefore 40% (remaining) = 320 mins (using unitary method)

320 mins = 5 hrs 20 mins

nave · Answer

I tried using just ratios to solve this (because rate is constant):

8Hrs to fill 3/5 tank i.e 0.6 of the tank
X hrs to fill 2/5 tank i.e 0.4 of the tank

=> 8/0.6 = X/0.4
=> X=3.2/0.6 = 32/6 = 16/3 = 5.33hrs i.e 5hr20min

Pretz · Answer

As per what I did,

8 Hours - 3/5 of capacity
? Time - to fill remaining - 2/5 of capacity.

But the answer I am getting is incorrect. Could someone share the appropriate process to work on this?

EMPOWERgmatRichC · Answer

Hi Pretz,

There are a couple of different ways to approach the math in this question. It looks like you started to set up a ratio, but didn't complete the work. Here's one way to go about it:

Since it takes 8 hours to fill 3/5 of the pool and X hours to fill 2/5 of the pool.....

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

Since both fractions are "over 5", we can multiply those 5s out (by multiplying the numerator and denominator by 5)....

8/X = 3/2

Now we can cross-multiply and solve for X....

16 = 3X
16/3 = X
5 1/3 hours = X

5 1/3 hours = 5 hours 20 minutes

Final Answer:  B

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

IanStewart · Answer

If it takes 8 hours to fill 3/5 of the pool, then
it takes 8/3 hours to fill 1/5 of the pool, and 
it thus takes 16/3 hours to fill 2/5 of the pool, which is what we need to do.

OptimusPrepJanielle · Answer

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?

(3/5) 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?
(3/5) of a pool/ 8 hours = 3/40 (the rate)

(3 pools/40 hours) = (2/5* pool)/ x hours 
Cross multiply 3x = (2/5) 40
3x = (2/ 5 ) (8) ( 5 )
3x = 16
x = 16/3 or 5 1/3
1/3 of an hour = 20 minutes

* The pool is 3/5 full so 2/5 remains.

(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

JeffTargetTestPrep · Answer

Solution:

To solve we can setup a proportion. The proportion will read:

A time of 8 hours is to filling up 3/5 of the pool is the same as a time of x number of hours is to filling up (the remaining) 2/5 of the pool. Setting this up mathematically we have:

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

40/3= 5x/2

Cross multiplying, we get:

80 = 15x

16 = 3x

16/3 = x

5 1/3 hours = x

5 hours and 20 minutes = x

Answer: B

generis · Answer

45-second approach: Find rate of filling. Find work remaining. Find time needed to finish: Work divided by rate equals time (to fill volume that needs filling).

What is rate of filling? 
  \frac{Work}{time} = rate

RATE =  \frac{(\frac{3}{5})}{8} = (\frac{3}{5}*\frac{1}{8})= \frac{3}{40}

How much work remaining?
 1 - (\frac{3}{5}) = (\frac{5}{5} - \frac{3}{5})= \frac{2}{5}

How much time to finish remaining work?   \frac{Work}{rate} = time

Work remaining =  \frac{2}{5} 
Rate =  \frac{3}{40}

\frac{(\frac{2}{5})}{(\frac{3}{40})}  =

\frac{2}{5} *
\frac{40}{3} = 5\frac{1}{3}hrs

Multiply  any  fraction of an hour by 60 to get minutes.* In cases where you already have the hours, and you need hours plus minutes, use  only  the fraction. (Do not include the 5 here.)

\frac{1}{3}hr * 60 =  20 minutes

5\frac{1}{3}hrs  = 5 hours, 20 minutes

Answer B

* Because:

\frac{1hr}{3} * \frac{60min}{1hr} =  20 minutes, where hours cancel

EMPOWERgmatRichC · Answer

Hi All,

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:

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

ScottTargetTestPrep · Answer

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

MHIKER · Answer

3/5 full in 8 hours (rest = 1-(3/5) = 2/5)
2/5 is filled in (8*5*20)/3*5 = 8 hour 20 minutes

Abhishek009 · Answer

Let the capacity of the pool be  40  Units ( LCM of 5 & 8)

So, in 8 Hours the pipe fills  24  units; Thus efficiency of the pipe is 3units/Hour

Time required to fill the entire pool is  \frac{16}{3}  hours =  5\frac{1}{3} = 5 Hours 20 Min ; Answer must be (B)

msu6800 · Answer

3/5 of the capacity takes =8 hours
So whole capacity will take =8*(5/3)=40/3 hours
More times needed=(40/3)-8=16/3= 5 hours 20 minutes.

Posted from my mobile device

ArnauG · Answer

Let the total capacity of the pool be represented by C. Then, the pool is filled to 3/5C in 8 hours, which means that the rate of filling is (3/5)C/8.

To fill the remaining 2/5 of the pool, we need to determine how much time it will take at this same rate. Let t be the additional time needed to fill the pool completely, then we have:

(3/5)C/8 × t = 2/5 C

Solving for t, we get:

t = (2/5 C) /   = 16/3 hours = 5 hours and 20 minutes

Therefore, the answer is (B) 5 hr 20 min.

hkalabdu · Answer

T ( Time) = 8 hours + X >> x is the extra time that we are calculating

R ( Rate) = 3/5/8 = 3/5 * 1/8 = 3/40

W ( work needs to be completed ) In this problem half of the work is completed and we want to complete the remaining work to make it complete aka =1

T*R=W

8+x * 3/40x = 1

Once we multiply the above equation by 40 and simplify we get 15x = 80

x = 80/15 = 16/3 = 5 and reminder of 1/3. We multiply the remainder by 60 minutes. The final answer is 5 hours and 20 minutes

bumpbot · Answer

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.

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

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Problem Solving (PS) Questions

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

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards