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# A, B, C have constant rates. Pumps A & B can fill a tank

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Intern
Joined: 22 Mar 2007
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A, B, C have constant rates. Pumps A & B can fill a tank [#permalink]

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20 May 2007, 15:34
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

A, B, C have constant rates. Pumps A & B can fill a tank in 6/5 hours. Pumps A & C can fill a tank in 3/2 hours. Pumps B & C can fill a tank in two hours. How many hours does it take all 3 working together to fill the tank?

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Senior Manager
Joined: 03 May 2007
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Re: GMAT Prep: Rate problem [#permalink]

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20 May 2007, 17:13
skinsvt wrote:
A, B, C have constant rates. Pumps A & B can fill a tank in 6/5 hours. Pumps A & C can fill a tank in 3/2 hours. Pumps B & C can fill a tank in two hours. How many hours does it take all 3 working together to fill the tank?

you have three equations and three unknowns.
i have never tried this way but let's see if it works

1/A+1/B=5/6
1/A+1/C=2/3
1/B+1/C=1/2

2/A+2/B+2/C=5/6+4/6+3/6 divide both parts by 2

1/A+1/B+1/C=12/12

Last edited by Sergey_is_cool on 20 May 2007, 18:00, edited 1 time in total.

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20 May 2007, 17:56
oa from gmatprep is 1

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Senior Manager
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20 May 2007, 17:59
oops I guess i can add numbers 5+4+3 is 12 not 13

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20 May 2007, 18:01
thanks this one was driving me nuts

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20 May 2007, 18:04
skinsvt wrote:
thanks this one was driving me nuts

thank you. Because of this problem I found the fast way to solve rate problems in 1 minute

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20 May 2007, 18:04
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