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

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An empty pool being filled with water at a constant rate tak [#permalink]

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07 Feb 2011, 01:20
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An empty pool being filled with water at a constant rate takes 8hours to fill to 3/5 of its capacity.how much more time will it take to finish filling the pool?

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

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07 Feb 2011, 01:27
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3/5 pool -> 8 hours
1 pool -> 8/(3/5) h
1 pool -> 40/3 h

So, it takes 40/3 hours to fill the entire pool but 8 hours out of 40/3 are already spent.

40/3 = 8 + x
x = (40/3) - 8 = 16/3 hours left to fill the entire pool

16/3 hours = 5hours 20minutes

Ans: "B"
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07 Feb 2011, 03:44
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GMATD11 wrote:
An empty pool being filled with water at a constant rate takes 8hours to fill to 3/5 of its capacity. how much more time will it take to finish filling the pool?
a)5hr 30min
b)5hr 20min
c)4hr 48min
d)3 hr 12min
e) 2hr 40 min

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

To fill 3/5 of the pool took 8 hours --> to fill 2/5 of the pool will take 8/(3/5)*2/5=16/3 hours = 5 hours 20 minutes (because if t is the time needed to fill the pool then t*3/5=8 --> t=8*5/3 hours --> to fill 2/5 of the pool 8*5/3*2/5=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 = job/rate = 2/(3/8) = 16/3 hours = 5 hours 20 minutes.

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08 Feb 2011, 06:32
Bunuel wrote:
GMATD11 wrote:
An empty pool being filled with water at a constant rate takes 8hours to fill to 3/5 of its capacity. how much more time will it take to finish filling the pool?
a)5hr 30min
b)5hr 20min
c)4hr 48min
d)3 hr 12min
e) 2hr 40 min

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

To fill 3/5 of the pool took 8 hours --> to fill 2/5 of the pool will take 8/(3/5)*2/5=16/3 hours = 5 hours 20 minutes (because if t is the time needed to fill the pool then t*3/5=8 --> t=8*5/3 hours --> to fill 2/5 of the pool 8*5/3*2/5=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 = job/rate = 2/(3/8) = 16/3 hours = 5 hours 20 minutes.

Thanks Bunuel
using this capacity left to fill in solution i can save time
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Updated on: 11 Jun 2011, 00:08
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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

Originally posted by sudhir18n on 11 Jun 2011, 00:05.
Last edited by sudhir18n on 11 Jun 2011, 00:08, edited 2 times in total.
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11 Jun 2011, 10:47
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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
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Re: An empty pool being filled with water at a constant rate tak [#permalink]

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30 May 2013, 05:10
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Re: An empty pool being filled with water at a constant rate tak [#permalink]

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05 Jun 2013, 15:04
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I did this a little differently.
It takes 480 mins to fill 3/5 of the pool.
We're trying to find out how long it'll take for the remaining 2/5.
I solved how many minutes it'll take to fill the pool to 1/5 capacity and multiplied it by 2.
480 / 3 = 160 mins (1/5 full)
160 * 2 = 320 mins (2/5 full)
320 mins = 5 hours 20 mins
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An empty pool being filled with water at a constant rate tak [#permalink]

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28 Jan 2017, 11:24
Bunuel wrote:
GMATD11 wrote:
An empty pool being filled with water at a constant rate takes 8hours to fill to 3/5 of its capacity. how much more time will it take to finish filling the pool?
a)5hr 30min
b)5hr 20min
c)4hr 48min
d)3 hr 12min
e) 2hr 40 min

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

To fill 3/5 of the pool took 8 hours --> to fill 2/5 of the pool will take 8/(3/5)*2/5=16/3 hours = 5 hours 20 minutes (because if t is the time needed to fill the pool then t*3/5=8 --> t=8*5/3 hours --> to fill 2/5 of the pool 8*5/3*2/5=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 = job/rate = 2/(3/8) = 16/3 hours = 5 hours 20 minutes.

it took 8 hours to fill 3/5 of pool. Can't we consider it would have taken 2 hours to fill 1/5th of pool as rate is constant. so it will take 4hours to fill remaining 2/5th of pool ?
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Re: An empty pool being filled with water at a constant rate tak [#permalink]

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28 Jan 2017, 11:29
ammuseeru wrote:
Bunuel wrote:
GMATD11 wrote:
An empty pool being filled with water at a constant rate takes 8hours to fill to 3/5 of its capacity. how much more time will it take to finish filling the pool?
a)5hr 30min
b)5hr 20min
c)4hr 48min
d)3 hr 12min
e) 2hr 40 min

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

To fill 3/5 of the pool took 8 hours --> to fill 2/5 of the pool will take 8/(3/5)*2/5=16/3 hours = 5 hours 20 minutes (because if t is the time needed to fill the pool then t*3/5=8 --> t=8*5/3 hours --> to fill 2/5 of the pool 8*5/3*2/5=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 = job/rate = 2/(3/8) = 16/3 hours = 5 hours 20 minutes.

it took 8 hours to fill 3/5 of pool. Can't we consider it would have taken 2 hours to fill 1/5th of pool as rate is constant. so it will take 4hours to fill remaining 2/5th of pool ?

HOW did you get this?

8 hours to fill 3/5 of pool
So, to fill 1/5th of the pool it'll take 3 times less, so 8/3 hours. Therefore to fill 2/5th it'll take twice as much time, so 16/3 hours.
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Re: An empty pool being filled with water at a constant rate tak [#permalink]

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22 Oct 2017, 05:09
Lets assume tank capacity is 100 ml

So 8 hrs ----for 3/5*100 =60 ml
x hrs------40 ml

So ....8/60 = x/40

x= 5.30

where am i going wrong here?
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Re: An empty pool being filled with water at a constant rate tak [#permalink]

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22 Oct 2017, 05:49
santro789 wrote:
Lets assume tank capacity is 100 ml

So 8 hrs ----for 3/5*100 =60 ml
x hrs------40 ml

So ....8/60 = x/40

x= 5.30

where am i going wrong here?

Check arithmetic:

8/60 = x/40

x = 16/3.
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Re: An empty pool being filled with water at a constant rate tak [#permalink]

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22 Oct 2017, 06:21
thanks Bunuel but 16/3 =5.33 which would be equal to 5.30 then how come the answer is 5.20
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Re: An empty pool being filled with water at a constant rate tak [#permalink]

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22 Oct 2017, 06:30
santro789 wrote:
thanks Bunuel but 16/3 =5.33 which would be equal to 5.30 then how come the answer is 5.20

1/3rd of an hour is 20 minutes.
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An empty pool being filled with water at a constant rate tak [#permalink]

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22 Oct 2017, 10:34
GMATD11 wrote:
An empty pool being filled with water at a constant rate takes 8hours to fill to 3/5 of its capacity.how much more time will it take to finish filling the pool?

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

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

*Because:

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

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Re: An empty pool being filled with water at a constant rate tak [#permalink]

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28 Dec 2017, 07:12
Bunuel, niks18, amanvermagmat

How valid is this approach?
x = full capacity

Amount of work = Rate * no of hours
(3/5)*x = R1 *8 (first phase)
(2/5) *x = R2 * y (remaining phase/ capacity to fill)

Setting proportionality:

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

I am skipping extra steps since led to same answer choice, ie y = 16/3
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Re: An empty pool being filled with water at a constant rate tak [#permalink]

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28 Dec 2017, 10:53
GMATD11 wrote:
An empty pool being filled with water at a constant rate takes 8hours to fill to 3/5 of its capacity.how much more time will it take to finish filling the pool?

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

Whats wrong with my solution ?

8 = 3/5
x=2/5 cross multiply... but in the end I get 16/3 = 5,333
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Re: An empty pool being filled with water at a constant rate tak [#permalink]

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28 Dec 2017, 10:58
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Expert's post
dave13 wrote:
GMATD11 wrote:
An empty pool being filled with water at a constant rate takes 8hours to fill to 3/5 of its capacity.how much more time will it take to finish filling the pool?

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

Whats wrong with my solution ?

8 = 3/5
x=2/5 cross multiply... but in the end I get 16/3 = 5,333

Not sure what you are doing there but the answer you are getting is correct: 16/3 hours = 5 hours 20 minutes. This is explained in the solutions which are presented in this topic. It seems that you don't read the thread at all...
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Re: An empty pool being filled with water at a constant rate tak [#permalink]

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20 Feb 2018, 16:05
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

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Re: An empty pool being filled with water at a constant rate tak [#permalink]

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06 Mar 2018, 08:06
GMATD11 wrote:
An empty pool being filled with water at a constant rate takes 8hours to fill to 3/5 of its capacity.how much more time will it take to finish filling the pool?

A. 5hr 30min
B. 5hr 20min
C. 4hr 48min
D. 3 hr 12min
E. 2hr 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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Re: An empty pool being filled with water at a constant rate tak   [#permalink] 06 Mar 2018, 08:06
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