SOLUTION: An inlet pipe can fill a swimming pool in nine hours and an outlet pipe can empty a pool in 12 hours. Through an error both pipes were left open. How long will it take to fill the

Question 288966: An inlet pipe can fill a swimming pool in nine hours and an outlet pipe can empty a pool in 12 hours. Through an error both pipes were left open. How long will it take to fill the pool?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
An inlet pipe can fill a swimming pool in nine hours and an outlet pipe can empty a pool in 12 hours. Through an error both pipes were left open. How long will it take to fill the pool?
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Inlet DATA:
time = 9 hrs/job ; rate = 1/9 job/hr
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Outlet pipe DATA:
time = 12 hr/job ; rate = 1/12 job/hr
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Together DATA:
time = x hr./job ; rate = 1/x job/hr
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Equation:
rate - rate = together rate
1/9 - 1/12 = 1/x
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Multiply thru by 36x to get:
12x - 9x = 36
3x = 36
x = 12 hrs (time to fill the pool together)
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Cheers,
Stan H.
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