<PRE><B>Question 302994</B>
One inlet pipe can fill an empty pool in 4 hours, and a drain can empty the pool in 10 hours. How long will it take the pipe to fill the pool if the drain is left open? 
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Filling rate: 1/4 pool/hr
Emptying rate: 1/10 pool/hr
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Together rate: 1/x pool/hr
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Equation:
rate - rate = together rate
1/4 - 1/10 = 1/x
(10-4)/40 = 1/x
6/40 = 1/x 
x = 40/6 = 20/2 = 6 2/3 hrs (time to fill the pool
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cheers,
Stan H.</PRE>