SOLUTION: A tank can be filled in 9 hours by one pipe and in 12 hours by another. How long will it take both pipes to fill the empty tank?

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Question 826414: A tank can be filled in 9 hours by one pipe and in 12 hours by another. How long will it take both pipes to fill the empty tank?
Answer by josgarithmetic(39613) About Me  (Show Source):
You can put this solution on YOUR website!
Handle rates as amount of tank per hour. The rate is the sum of the rates of the individual pipes.

1%2F9%2B1%2F12=4%2F36%2B3%2F36=7%2F36

That rate means, 7 tanks in 36 hours. Flip this and say, 36 hours to fill 7 tanks. Compute how many hours per tank.