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# Pipe A will fill a tank in 24 minutes and pipe B will fill t

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Manager
Joined: 20 Nov 2009
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Pipe A will fill a tank in 24 minutes and pipe B will fill t [#permalink]

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29 Apr 2010, 12:07
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Pipe A will fill a tank in 24 minutes and pipe B will fill the same tank in 36 minutes. There is a drain pipe which will empty the tank in 30 minutes. If the drain pipe is opened 8 minutes after A and B are opened, when will the tank be full?
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Joined: 12 Jan 2010
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Schools: DukeTuck,Kelogg,Darden
Re: Pipes and cisterns -3 [#permalink]

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29 Apr 2010, 12:27
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aiming4mba wrote:
Pipe A will fill a tank in 24 minutes and pipe B will fill the same tank in 36 minutes. There is a drain pipe which will empty the tank in 30 minutes. If the drain pipe is opened 8 minutes after A and B are opened, when will the tank be full?

Hi Assume the Volume of tank is 360 ( i chose this because its the LCM of 24,30 and 36).

So flow of pipe A = 15 L/min
Flow of Pipe B = 10 l/min
Flow of drain pipe and pipe a and B are open = 25-12=13 L/Min

Flow when pipe A and B are open = 15+10 =25 L
Drain = 12 L/min

so 8 mins only and B are open volume filled = 25*8= 200 L.

So time required to fill the remaining volume (360-200) = 160 / 13

= 12.3 Mins

So Tank will fill up in 12 Mins and 18 seconds.
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Joined: 24 Jul 2009
Posts: 286
Re: Pipes and cisterns -3 [#permalink]

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29 Apr 2010, 12:28
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Let k be the time when both the filling and drain pipes were open.

8(1/24 + 1/36) + k(1/24 + 1/36 -1/30) = 1
k= 160/13

Total time = 8 + 160/13
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Re: Pipes and cisterns -3 [#permalink]

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29 Apr 2010, 12:33
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aiming4mba wrote:
Pipe A will fill a tank in 24 minutes and pipe B will fill the same tank in 36 minutes. There is a drain pipe which will empty the tank in 30 minutes. If the drain pipe is opened 8 minutes after A and B are opened, when will the tank be full?

in 8 minutes total filled = (1/24 + 1/30)*8 = 5/9

now a b c will together fill 4/9 of the rest

combine speed = 1/24 + 1/36 - 1/30 =13/360

now..... work = rate*time => time = 4/9 * 360/13 = 160/13

so total time = 8+160/13 = 20$$\frac{4}{13}$$
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Re: Pipes and cisterns -3 [#permalink]

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29 Apr 2010, 12:33
Im confused, do we need the total time or the time after the drain is open?
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Re: Pipes and cisterns -3 [#permalink]

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26 May 2014, 07:37
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Re: Pipe A will fill a tank in 24 minutes and pipe B will fill t [#permalink]

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14 Oct 2015, 11:33
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).

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Re: Pipe A will fill a tank in 24 minutes and pipe B will fill t [#permalink]

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04 May 2017, 11:08
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).

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Re: Pipe A will fill a tank in 24 minutes and pipe B will fill t [#permalink]

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04 May 2017, 13:24
aiming4mba wrote:
Pipe A will fill a tank in 24 minutes and pipe B will fill the same tank in 36 minutes. There is a drain pipe which will empty the tank in 30 minutes. If the drain pipe is opened 8 minutes after A and B are opened, when will the tank be full?

let m=minutes to fill pool
m(5/72)-(m-8)/30=1
m=264/13=20.3 minutes
Re: Pipe A will fill a tank in 24 minutes and pipe B will fill t   [#permalink] 04 May 2017, 13:24
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