The pool can be filled with water through the first pipe in 6 hours

The pool can be filled with water through the first pipe in 6 hours, and the second in 10 hours. What part of the pool will remain empty after 1 hour if both pipes are opened?

For 1 hour, 1/6 of the pool is filled with water through the first pipe, and 1/10 of the pool through the second.
After 1 hour, 1 – (1/6 + 1/10) = 1 – (5/30 + 3/30) = 1 – 4/15 = 11/15 part of the pool will remain unfilled.
Answer: 11/15.