<PRE><B>Question 828199</B>
A pipe can fill a water tank at X hours. Another pipe can fill a water tank at Y hours. If both pipe are used to fill the tank, how many hours would it take?
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1st pipe rate: 1/x job/hr
2nd pipe rate: 1/y job/hr
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Together rate = 1/x+1/y = (x+y)/xy job/hr
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Together time = xy/(x+y) hours/job
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Cheers,
Stan H.</PRE>