SOLUTION: A water tank can be filled in 7 minutes and emptied in 9 minutes. If the drain is accidentally left open when the tank is being filled, how long does it take to fill the tank?

Question 245699: A water tank can be filled in 7 minutes and emptied in 9 minutes. If the drain is accidentally left open when the tank is being filled, how long does it take to fill the tank?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
A water tank can be filled in 7 minutes and emptied in 9 minutes. If the drain is accidentally left open when the tank is being filled, how long does it take to fill the tank?
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Filling rate = 1/7 tank/min
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Emptying rate = 1/9 tank/min
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Let the time to fill the tank be "x".
Together rate = 1/x tank/min
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Equation:
rate - rate = together rate
1/7 - 1/9 = 1/x
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9x - 7x = 7*9
2x = 63
x = 31.5 hrs (# of hrs. required to fill the tank)
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Cheers,
Stan H.
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