Question 8
Exercise 4. A tank has three pipes. The first pipe can fill $\frac12$ of the tank in 1 hour while the second pipe can fill $\frac13$ part in 1 hour. The third pipe is used for making the tank empty. When all three pipes are open, $\frac7{12}$ part of the tank is filled in 1 hour. How much time will the third pipe take to empty the completely filled tank alone?
**Editorial input convention:** Assume all flow rates are constant while water is available, with no other flows. Enter the outlet-alone time in hours.
**Editorial input convention:** Assume all flow rates are constant while water is available, with no other flows. Enter the outlet-alone time in hours.