Question 204261
Try this:
If the hose can fill the pond in 2 hours, then it can fill 1/2 the pond in 1 hour.
If the drain can empty the pond in 3 hours, then it can empty 1/3 of the pond in 1 hour.
Together, the hose and drain can fill: {{{1/2-1/3 = 1/6}}} of the pond in 1 hour.
Therefore, it will take 6 hours to fill the pond.