Pipe P fills a tank in 12 hours and pipe Q in 16 hours. Both are opened together, but Q is turned off after a while, and the tank is full exactly 9 hours after the start. For how many hours was Q open?

Question

Accepted Answer

4. P runs all 9 hours and fills 9/12 = 3/4 of the tank. Q fills the other 1/4: t/16 = 1/4, so t = 4 hours.

Pipe P fills a tank in 12 hours and pipe Q in 16 hours. Both are opened together, but Q is turned off after a while, and the tank is full exactly 9 hours after the start. For how many hours was Q open?

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