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GMAT Prep--Rate

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GMAT Prep--Rate

by mindruna » Mon Jul 30, 2007 6:27 pm
Ok guys, I've tried this one to the best of my (somewhat feable) abilities, but I still don't get it.

Pumps A,B,C, operate at their respective constant rates. Pumps A and B, operating simultaneously, can fill a tank in 6/5 hours, A and C in 3/2 hours and B and C in 2 hours. How many hours does it take pumps A, B, and C operating simultaneously to fill the tank?

The correct answer is 1. I have no idea how to get that...

Thanks in advance for helping me out.
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by givemeanid » Mon Jul 30, 2007 6:44 pm
1/A + 1/B = 1/(6/5) = 5/6
1/A + 1/C = 2/3
1/B + 1/C = 1/2

Add all of them:
2(1/A + 1/B + 1/C) = 5/6 + 2/3 + 1/2 = 2
1/A + 1/B + 1/C = 1
So It Goes
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thanks.

by mindruna » Mon Jul 30, 2007 6:53 pm
You make it so simple givemeanaid! Thank you!
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question

by Atult718 » Mon Jul 30, 2007 10:53 pm
Hey,

I followed till 1/a+1/b+1/c = 2

how did you get 2(1/a+1/b+1/c) ?
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Re: question

by givemeanid » Tue Jul 31, 2007 5:35 am
Atult718 wrote:Hey,

I followed till 1/a+1/b+1/c = 2

how did you get 2(1/a+1/b+1/c) ?
If you add all the left hand sides and right hand sides of the 3 equations, you will see each of 1/A, 1/B, and 1/C comes up twice.
So It Goes
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