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# There are two pumps X and Y. To empty a water tank, X

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Director
Joined: 14 Sep 2005
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Location: South Korea
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There are two pumps X and Y. To empty a water tank, X [#permalink]  25 Nov 2005, 05:28
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There are two pumps X and Y.

To empty a water tank, X takes 24 hours.

Y works at 2/3 speed of X.

X has been emptying the water tank for 8 hours.

How many hours does it take for Y to completely empty the water tank?
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Director
Joined: 24 Oct 2005
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Location: London
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X takes 24 hrs
In 1 hr, it does 1/24 of the work.
In 8 hrs it does 8/24 work = 1/3

Remaining work = 2/3
Y's rate is 2/3 of X, so in 1 hr, Y can do (2/3)*(1/24) = 1/36 of the work in 1 hr
To do the remaining 2/3 of the work working at rate of 1/36, Y will take

(2/3 ) / (1/36) = 24 hrs
Current Student
Joined: 29 Jan 2005
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Re: PS - Pumps [#permalink]  25 Nov 2005, 06:45
gamjatang wrote:
There are two pumps X and Y.

To empty a water tank, X takes 24 hours.

Y works at 2/3 speed of X.

X has been emptying the water tank for 8 hours.

How many hours does it take for Y to completely empty the water tank?

Another method:

T(X)=24
T(Y)=4/3*24=32

32-8 (work completed)=24
VP
Joined: 30 Sep 2004
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Location: Germany
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Re: PS - Pumps [#permalink]  25 Nov 2005, 07:23
GMATT73 wrote:

Another method:

T(X)=24
T(Y)=4/3*24=32

32-8 (work completed)=24

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Re: PS - Pumps   [#permalink] 25 Nov 2005, 07:23
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