There is 7350 ml of water in a fish tank. The water is leaking at a rate of 320 ml per minute. If, at the same time, water is added into the tank at a rate of 170 ml per minute, how long will it take to empty the tank?
The net loss of water from the fish tank is 320 170 = 150 ml per min.
So the real leaking rate is 150 ml/min.
Thus, the time needed: 7350 ÷ 150 = 49