SOLUTION: A tank can be filled by one pipe in 12 hours, by a second pipe in 7 hours, and by a third pipe in 4 hours. If all three pipes are open, how long will it take to fill the tank.

Question 937613: A tank can be filled by one pipe in 12 hours, by a second pipe in 7 hours, and by a third pipe in 4 hours. If all three pipes are open, how long will it take to fill the tank.
Answer by nerdybill(7384) (Show Source): You can put this solution on YOUR website!
A tank can be filled by one pipe in 12 hours, by a second pipe in 7 hours, and by a third pipe in 4 hours. If all three pipes are open, how long will it take to fill the tank.
.
Let t = time (hours) it takes to fill tank
then
t(1/12 + 1/7 + 1/4) = 1
multiply both sides by 84:
t(7 + 12 + 21) = 84
t(40) = 84
t = 2.1 hours
or
t = 2 hours and 6 minutes
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