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cveluswamy
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 Posted: Sat Aug 04, 2007 11:45 am Post subject: GMATPREP Constant Rate |
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At a constant Rate of flow, it takes 20 minutes to fill a swimming pool if a large hose is used and 30 minutes if a small hose is Used. At these constant rates, how many minutes will it take to fill the pool when both hoses are used simultaneously?
A. 10
B. 12
C. 15
D. 25
E. 50 |
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jayhawk2001
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| Posted: Sat Aug 04, 2007 2:54 pm Post subject: |
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You have to use the rate formula here
1/t = 1/t1 + 1/t2 = 1/30 + 1/20 = 1/12
So, 12 minutes
Put another way, in each minute the pipes can fill 1/30 and 1/20 of the
pool respectively. So, combined the hoses can fill (1/30 + 1/20) of the
pool per minute. The reciprocal of this value will give you the time
required to fill the pool when both hoses are used. |
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