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# Pipe A can fill a tank in 12 hours. Pipe B whose diameter is

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VP
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Pipe A can fill a tank in 12 hours. Pipe B whose diameter is [#permalink]

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03 Jan 2006, 22:17
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Pipe A can fill a tank in 12 hours. Pipe B whose diameter is twice that of pipe A is also connected to the tank. If both the pipes are kept open when the tank is empty, how long will it take the tank to overflow?
(A)2 hours 40 minutes
(B)2 hours 12 minutes
(C)4 hous
(D)9 hours 36 minutes
(E)2 hours 24 minutes
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04 Jan 2006, 03:21
Straight E.

Pipe B will fill the tank 4 times faster than A.

So ANS = 12/5 i.e 2 Hour 24 minutes
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04 Jan 2006, 11:22
diameter of 2nd pipe is twice the first so it will fill 4 time faster than the first .

so it will take 3 hrs to fill

so total time taken is 1/(1/12 + 1/3) = 12/5 = 2 hrs 24 mins .

Ans E.
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07 Jan 2006, 00:48
twice the diameter=>twice the radius=>4 times the volume=>1/4 of time taken
So A= 12 hrs B= 3 hrs

total time =1/(1/12+1/3)=12/5=2hrs 24min
VP
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08 Jan 2006, 12:14
Thanks guys! OA is E.
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"To dream anything that you want to dream, that is the beauty of the human mind. To do anything that you want to do, that is the strength of the human will. To trust yourself, to test your limits, that is the courage to succeed."

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21 Feb 2006, 15:43
andy_gr8 wrote:
twice the diameter=>twice the radius=>4 times the volume=>1/4 of time taken
So A= 12 hrs B= 3 hrs

total time =1/(1/12+1/3)=12/5=2hrs 24min

Hi Andy_gr8
Can you please explain this -- if the radius is 4 times then => volume be 8 times??
Thanks
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21 Feb 2006, 22:33
andy_gr8 wrote:
twice the diameter=>twice the radius=>4 times the volume=>1/4 of time taken
So A= 12 hrs B= 3 hrs

total time =1/(1/12+1/3)=12/5=2hrs 24min

God bless Andy..
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21 Feb 2006, 22:53
Pipe A - 1/12 tank in 1 hour

Area = pi * r^2
Area of B = pi * (2r)^2 = pi * 4r^2 --> B is 4 times faster

Pipe B - 1/3 tank in 1 hour

Together, 5/12 tank in 1 hour ---> 1 tank in 12/5 hours = 144 minutes = 2 hours 24 mins
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22 Feb 2006, 08:17
Hi-
Just curious - Where is this question from? The wording seems to be a bit ambiguous to be an offical GMAT question.
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