A tank is currently filled to two-fifths of its capacity. Pipe A can fill the tank completely in 10 minutes, while pipe B can drain it entirely in 6 minutes. If both pipes are opened simultaneously, how long will it take to either fill or empty the tank entirely?

Explanation

Since pipe B empties the tank faster than pipe A fills it, the tank will be emptied. The fraction of the tank to be emptied is 2/5. The net emptying rate when both pipes are open is (1/6 - 1/10) = 1/15 of the tank per minute. Using the ratio 1/15 : 2/5 = 1 : x, solving for x gives x = (2/5) * 15 = 6 minutes. Therefore, the tank will be completely emptied in 6 minutes.