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A pool can be filled in 4 hours and drained in 5 hours. The

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New post 22 Aug 2015, 19:05
pool can be filled in 4 hours and drained 5 hours.
take lcm of two pipes that is 20 units.
takes 20 hours to fill pool if both the pipes opened simultaneously.

filling pipe can fill 5units/hour.

draing pipe take out 4units?hour.
pool was opened at 1 pm.
pool was filled at 11 pm. It takes 10 hours to complete it.

If drain pipe opened at 2 pm. filling pipe worked for 1 hour. so 5units work over.
remaining 15 units take additional 15 hours to fill.
if drain pipe opened at 2.30pm. filling pipe worked for 1 and 1/2 hour 7.5 units work over.
take 12. 5 units , take additional 12.5 hours to fill.
if drain pipe opened at 3 pm, 10 units units, over, 10 hours to fill.
if drain pipe opened at 3.30pm. 12.5 units over, another 7.5 units , hours take to fill.
3.30+7.30= 11pm
so option D is correct
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New post 26 Aug 2015, 08:09
10/4 - x/5 = 1 not 1/10
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New post 25 Nov 2015, 03:52
Economist wrote:
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

A pool can be filled in 4 hours and drained in 5 hours. The valve that fills the pool was opened at 1:00 pm and some time later the drain that empties the pool was also opened. If the pool was filled by 11:00 pm and not earlier, when was the drain opened?

A. at 2:00 pm
B. at 2:30 pm
C. at 3:00 pm
D. at 3:30 pm
E. at 4:00 pm

[Reveal] Spoiler:
I did:
10/4 - x/5 = 1/10 ( x = number of hours drain pipe is opened ). But I cant find the answer.


m20 q32


I would rather use here smart numbers....
Pool Capacity = 100 Liters
Filling Rate (F) = \(\frac{100}{4}=25\)
Draining Rate (D) = \(\frac{100}{5}=20\)
Time =10 Hours (Start 1:00 pm End 11:00 pm)

250 Liters were filled in 10 hours --> 10*Rate(F) so we have +150 Liters that must be drained (because the filled pool must have only 100 Liters)
\(Rate (D) * t = 150\) --> \(20*t=150\), \(t=7.5 Hours\)
Answer D (11 pm - 7.5 =3:30)

Hope this approach helps....
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Re: A pool can be filled in 4 hours and drained in 5 hours. The   [#permalink] 19 Jan 2018, 10:23

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