Question: If a tank can be filled by a pipe in 6 hours and another pipe can empty it in 4 hours, how long will it take to fill the tank if both pipes are opened together?
Options:
Correct Answer: 3 hours
Solution:
The net rate is 1/6 - 1/4 = 2/12 - 3/12 = -1/12. Therefore, the tank will never fill.