SOLUTION: The fill pipe for a tank can fill the tank in 4 hours, and the drain pipe can drain it in 2 hours. If both pipes are accidentally opened, how long will it take to empty a half-fill

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Question 489531: The fill pipe for a tank can fill the tank in 4 hours, and the drain pipe can drain it in 2 hours. If both pipes are accidentally opened, how long will it take to empty a half-filled tank?
Answer by ankor@dixie-net.com(15646) About Me  (Show Source):
You can put this solution on YOUR website!
The fill pipe for a tank can fill the tank in 4 hours, and the drain pipe can drain it in 2 hours.
If both pipes are accidentally opened, how long will it take to empty a half-filled tank?
:
Let t = time to empty the tank with both valves open
Let an empty tank = 1
then a half empty tank = .5
:
t%2F2 - t%2F4 = .5
multiply 4, results:
2t - t = 4(.5)
t = 2 hrs to empty the tank