SOLUTION: 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?

Question 92380: 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?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
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.
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