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A hotel began draining its swimming pool at a constant rate at 7am. Be

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A hotel began draining its swimming pool at a constant rate at 7am. Be  [#permalink]

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New post 17 Feb 2017, 03:07
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A hotel began draining its swimming pool at a constant rate at 7am. Beginning at 12pm, the rate tripled because of evaporation. If the pool began completely full and was 3/4 full at 9:30am, at what time was the pool completely empty?

A. 12:45pm
B. 1:20pm
C. 1:40pm
D. 2:10pm
E. 2:15pm

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Re: A hotel began draining its swimming pool at a constant rate at 7am. Be  [#permalink]

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New post 17 Feb 2017, 03:34
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Bunuel wrote:
A hotel began draining its swimming pool at a constant rate at 7am. Beginning at 12pm, the rate tripled because of evaporation. If the pool began completely full and was 3/4 full at 9:30am, at what time was the pool completely empty?

A. 12:45pm
B. 1:20pm
C. 1:40pm
D. 2:10pm
E. 2:15pm


let the quantity of water in the swimming pool be x
so at 7 am it is x and at 9:30 am it is 3x/4 Therefore constant draining rate = 0.25x/150mins

At 12 the pool will be half full i.e. x/2 (since x/4 will be drained from 9:30 to 12pm)
Also at 12pm the rate gets tripled, new draining rate = (3*0.25x)/150 = 0.75x/150

if 3/4 of the pool is emptied in 150 mins then to empty the remaining half of the pool i.e. x/2 will take t mins. So

0.75x/100 = 0.5x/ t
t= (0.5x*150)/0.75x = 100 mins
adding 100 mins to 12pm will result in 1:40 pm

Hence Option C is correct.
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Re: A hotel began draining its swimming pool at a constant rate at 7am. Be  [#permalink]

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New post 17 Feb 2017, 04:08
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Answer : [C]

1/4 emptied in 2.5 hrs. 1/2 emptied in 5 hrs i.e. till 12PM.

draining rate = (1/4) / 2.5 part/hr = 1/10 part/hr
increased draining rate = 3/10 part /hr

time taken to drain 1/2 at increased draining rate = (1/2) / (3/10) hrs = 5/3 hrs = 1 hr 40 mins (after 12 PM)
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Re: A hotel began draining its swimming pool at a constant rate at 7am. Be  [#permalink]

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New post 23 Feb 2017, 10:30
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Bunuel wrote:
A hotel began draining its swimming pool at a constant rate at 7am. Beginning at 12pm, the rate tripled because of evaporation. If the pool began completely full and was 3/4 full at 9:30am, at what time was the pool completely empty?

A. 12:45pm
B. 1:20pm
C. 1:40pm
D. 2:10pm
E. 2:15pm


Since 1/4 of the pool was drained between 7 a.m. and 9:30 a.m. (or in 2.5 hours), the rate of drainage was:

rate = work/time

rate = (1/4)/2.5 = 1/10.

From 9:30 a.m. to 12 p.m. (or in another 2.5 hours), the amount of water that was drained was:

work = rate x time

work = 1/10 x 2.5 = 2.5/10 = 1/4.

By 12 p.m. the pool was 3/4 - 1/4 = 1/2 full.

Since the rate tripled after 12 p.m., the new rate is 3/10. Now we can determine how many hours it took to drain the rest of the pool.

time = work/rate

time = (1/2)/(3/10) = 10/6 = 5/3 = 1⅔ hours = 1 hour and 40 minutes.

Thus, the pool was completely empty at 1:40 p.m.

Answer: C
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Re: A hotel began draining its swimming pool at a constant rate at 7am. Be  [#permalink]

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New post 08 Mar 2017, 23:12
Bunuel wrote:
A hotel began draining its swimming pool at a constant rate at 7am. Beginning at 12pm, the rate tripled because of evaporation. If the pool began completely full and was 3/4 full at 9:30am, at what time was the pool completely empty?

A. 12:45pm
B. 1:20pm
C. 1:40pm
D. 2:10pm
E. 2:15pm


Official solution from Veritas Prep.

In this Work/Rate problem, you can start by calculating the constant rate. If between 7am and 9:30am the pool drained by \(\frac{1}{4}\) of its capacity, that means that the pool drained at a rate of \(\frac{1}{4}\) pool per 2.5 hours. That then means that the pool drained by \(\frac{1}{10}\) pool per hour during normal hours, and \(\frac{3}{10}\) pool per hour after noon.

Since there are 5 hours between 7am and noon, the pool had drained by \(5(\frac{1}{10})\) of its capacity by noon, so it was half full. In the next hour (12pm-1pm) it drained by \(\frac{3}{10}\) of its capacity, so by 1pm it had \(\frac{2}{10}\) left to drain. If it drained by \(\frac{3}{10}\) every hour, that means that it only needed \(\frac{2}{3}\) of an hour to finish draining, meaning that it would be done by 1:40pm. Answer choice C is correct.
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Re: A hotel began draining its swimming pool at a constant rate at 7am. Be  [#permalink]

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New post 09 Mar 2017, 01:09
Let the capacity be 1000. According to the question, 1/4th of the water i.e. 250 got drained in 150 minutes
rate =250/150 = 5/3

total time the swimming pool got drained with this rate from 7 am to 12 pm = 5*60 = 300 minutes

total water drained = 5/3*300 = 500
left water = 1000 - 500 = 500
as the rate tripled after 12pm, new rate will be 5/3 *3 = 5

time taken to drain rest of the water with this rate = 500/5 = 100 minutes = 1 hr 40 minutes.

hence the swimming pool will get evacuated by 1:40 pm

Option C

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Re: A hotel began draining its swimming pool at a constant rate at 7am. Be  [#permalink]

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New post 17 Apr 2018, 00:55
Bunuel wrote:
A hotel began draining its swimming pool at a constant rate at 7am. Beginning at 12pm, the rate tripled because of evaporation. If the pool began completely full and was 3/4 full at 9:30am, at what time was the pool completely empty?

A. 12:45pm
B. 1:20pm
C. 1:40pm
D. 2:10pm
E. 2:15pm



The hotel began draining the swimming pool(which was completely full) at 7 AM.

At 9:30 AM(2 hours 30 minutes later), the pool was 3/4th full (or) 1/4th of the pool was drained.
At 12:00 PM(2 hours 30 minutes later), working at the same rate, another 1/4th of the pool was drained.
Now, the pool was half full at 12 AM.

It has been given that the draining rate triples because of evaporation after 12 PM.
Initially, 5 hours(300 minutes) was needed to drain the pool to half its capacity,
at 3 times the rate, we would be needing \(\frac{300}{3} = 100\) minutes to drain the pool now.

Therefore, the pool was completely empty at 1:40 PM(Option C) - 100 minutes after 12 PM
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Re: A hotel began draining its swimming pool at a constant rate at 7am. Be &nbs [#permalink] 17 Apr 2018, 00:55
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