SOLUTION: The inlet pipe of an oil tank can fill the tank in 1 hour, 30 minutes. The outlet pipe can empty the tank in 1 hour. Find how long it takes to empty the full tank if both pipes are

Question 291185: The inlet pipe of an oil tank can fill the tank in 1 hour, 30 minutes. The outlet pipe can empty the tank in 1 hour. Find how long it takes to empty the full tank if both pipes are open. Show work.
Answer by ptaylor(2198) (Show Source): You can put this solution on YOUR website!
I will deal in minutes
Let x= time it takes to empty the full tank if both pipes are open
Then with both pipes open, the tank empties at the rate of 1/x tank per min
Inlet pipe fills at the rate of 1/90 tank per min
outlet pipe empties at the rate of 1/60 tank per min
So with both pipes open the tank empties at the rate of 1/60-1/90 tank per min
So:
1/60-1/90=1/x multiply each term by 180x
3x-2x=180
x=180 min or 3 hr-------time it takes to empty the full tank if both pipes are open
CK
In 180 min, inlet pipe fills(1/90)*180=2 tanks
In 180 min, outlet pipe empties (1/60)*180=3 tanks
so, 3-2=1 tank emptied
Hope this helps---ptaylor