Question 58486
hello. i'm kind of stuck on this work word problem and I was wondering if you could help me out. It says... 
The fill pipe can fill a tank in 3 hours and the drain pipe can drain the tank in 1 hour. If both pipes are accidently opened, how long will it take to empty a tank filled with water? 

a keep getting a negative answer, if you could explain this it would be helpful. Thanks!


rate at which the fill pipe fills =1/3 cu units per hour
rate at which the drain pipe drains =1 cu unit per hour (or all of it in 1 hour)

Rate at which the tank is emptied when both pipes are open equals the difference between the rate at which it empties and the rate at which it fills

1-1/3=2/3 cu units per hour.  So:

Rate at which the tank is emptied when both pipes are open =2/3 cu units per hour or 1 divided by 2/3 = 3/2 hour=1.5 hours

Hope this helps---ptaylor