SOLUTION: ive really got some great help from this site, however i just cant find the right problem to help with this one..thanks the inlet pipe of an oil tank can fill the tank in 1 hour

Question 14588: ive really got some great help from this site, however i just cant find the right problem to help with this one..thanks
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 a full tank if both pipes are open.
im guessing i have to convert into minutes instead of hours ...with 1/90 +1/60 = 180 the answer i get is 32 hours..is this right.. thanks to anyone who can help
Answer by Earlsdon(6294) (Show Source): You can put this solution on YOUR website!
Find the hourly rates of the inlet pipe and the outlet pipe..
If the inlet pipe can fill the tank in 1 hour 30 mins. (3/2 hour), then it can fill 2/3 of the tank in 1 hour.
The outlet pipe can empty the tank in 1 hour (2/2 hour = 3/3 hour).
Together, inlet rate - outlet rate = 2/3 - 3/3 = -1/3 hour. So the tank is emptying (-) at the rate of 1/3 of the tank per hour.
So, it will take 3 hours to completely empty the tank.
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