SOLUTION: If a pipe takes 8hours to fill a tank..... And another pipe takes 4 hours to empty the tank.... When both of the pipes are on....how much time will it take to fill the tank????.

Algebra ->  Rate-of-work-word-problems -> SOLUTION: If a pipe takes 8hours to fill a tank..... And another pipe takes 4 hours to empty the tank.... When both of the pipes are on....how much time will it take to fill the tank????.      Log On


   

Question 774651: If a pipe takes 8hours to fill a tank.....
And another pipe takes 4 hours to empty the tank....
When both of the pipes are on....how much time will it take to fill the tank????..
Answer by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
The rates are additive when both pipes are fully open at the same time.
Filling pipe, 1%2F8 tank per hour
Emptying pipe, -1%2F4 tank per hour

Combined Rate, %281%2F8-1%2F4%29 tank per hour. Notice very carefully that rate of filling is smaller than the rate of emptying. YOU CANNOT FILL THIS TANK WHEN BOTH PIPES ARE OPEN!!

Simplify to 1%2F8-2%2F8=highlight%28-1%2F8%29 tank/hour.
This tank will never fill when both pipes are open all the way.