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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, 00:20
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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
[Reveal] Spoiler: OA

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07 Feb 2011, 00:27
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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, 02:44
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Expert's post
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, 05:32
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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08 Feb 2011, 11:16
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26 Feb 2011, 19:16
2/5th pool is left.
8 * 5/3 = time to fill full pool
8 * 5/3 * 2/5 = time to fill 2/5th pool = 16/3 hrs
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10 Jun 2011, 22:57
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 ?

5hr 30 min
5hr 20 min
4hr 48 min
3hr 12 min
2hr 40min

Sol:
Rate = (3/5 capacity) / 8 hours = (2/5 capacity) / x hours
solving for x : x = 80/15 = 5.3333 hr
i selected A which is 5hrs 30 min but original answer is 5hrs 20min .
Whats going wrong ?? isn't it 5.333... is 5hrs 30min when rounded off ??
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10 Jun 2011, 23:05
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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

Last edited by sudhir18n on 10 Jun 2011, 23:08, edited 2 times in total.
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10 Jun 2011, 23:06
But original answer is 5hr 20min Not 5hr 30min ..
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10 Jun 2011, 23:21
it means 5.33 is hours. and we have to convert 0.33hrs into minutes.... Thanks
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11 Jun 2011, 02:02
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8 x 5/3 x 2/5 = 5 and 1/3rd..which is 5hrs 20 mins..
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11 Jun 2011, 05:03
Rate = ((3/5)V)/8 hours

This rate is equal to the rate in filling the full volume of the pool.

((3/5)V/8hrs) = V/t hrs

3/40 = 1/t hrs

t = 40/3 hrs (time to fill the pool from empty to full)

Answer: 40/3 hours - 8 hours = 5 1/3 hours

Hence (B) 5 hours and 20 minutes
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11 Jun 2011, 09:47
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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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11 Jun 2011, 09:56
it takes 8 hours to fill 3/5 of the capacity

=> total capacity can be filled in 8c/(3c/5) = 40/3

=> additional time need to fill = 40/3 - 8

=> 13 hr 20 mins - 8 hrs = 5 hr 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, 04:10
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Re: An empty pool being filled with water at a constant rate tak [#permalink]

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02 Jun 2013, 13:26
8 hrs to fill 3/5th of the pool so how many hrs to fill the remainder (1- 3/5) i.e. 2/5th of the pool?

Cross multiply :

8 3/5

? 2/5

8 * 2/5 * 5/3 = 16/3 = 5 1/3 = 5 hrs and 20 mins
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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, 14:04
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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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Re: An empty pool being filled with water at a constant rate tak [#permalink]

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12 Sep 2013, 10:31
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

Sol:
work done in 1 hour: (3/5)/8 = 3/40

how much is left? (2/5)

Therefore, hours taken to complete this: (3/5)/(3/40) = 80/15 = 5 hours + (5/15) mins

5/15 in minutes = 5*4/15*4 = 20/60.

So, the answer is, 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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09 Jan 2015, 19:40
First convert 8 hrs to 480 min

Assume pool capacity = 100 lit
3/5 (100) = 60 lit

For 60 lit, it takes 480 min
So for 40 lit, it takes x

Cross-multiply:

(480 x 40)/60 = 320 min i.e. 5 hrs 20 min

Re: An empty pool being filled with water at a constant rate tak   [#permalink] 09 Jan 2015, 19:40

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