SOLUTION: 2 pipes are connected to a tank. On pipe fills the tank in 7 hours. The second pipe empties the tank in 9 hours. If both pipes are open, how long will it take to fill the tank?

Question 380404: 2 pipes are connected to a tank. On pipe fills the tank in 7 hours. The second pipe empties the tank in 9 hours. If both pipes are open, how long will it take to fill the tank?
Answer by Earlsdon(6294) (Show Source): You can put this solution on YOUR website!
Find the hourly rate of each event.
If the first pipe can fill the tank in 7 hours, then it can fill (+) of the tank in 1 hour.
If the second pipe can empty the tank in 9 hours, then it can empty (-) of the tank in 1 hour.
Putting these two events together, we get:

So of the tank is filled in 1 hour.
It takes hours to fill the tank.

hours.
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