One tap can fill a tank in 8 hours, while another tap can drain it in 16 hours. If both taps are operated at the same time, how long will it take to fill the tank?

Explanation

The filling tap fills 1/8 of the tank per hour, and the draining tap empties 1/16 of the tank per hour. Therefore, the net filling rate is 1/8 minus 1/16, which equals 1/16 of the tank per hour. Hence, the tank will be completely filled in 16 hours.