<PRE><B>Question 92380</B>
a faucet can fill a tub in 20 minutes, a drain can empty that same tub in 40 minutes if both the faucet and drain are open, how long will it take to fill the tub?
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Faucet DATA:
Time = 20 min/job ; Rate = 1/20 job/min
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Drain DATA:
Time = 40 min/job ; Rate = 1/40 job/min
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Together DATA;
Time = x min/job ; Rate = 1/x job/min

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EQUATION:
rate fill - rate empty = rate together
1/20 - 1/40 = 1/x
Multiply thru by 40x to get:
2x-x = 40
x = 40 min (Time to fill if the faucet is open and the drain is open)
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Cheers,
Stan H.</PRE>