Question 251699
First, find the hourly rate of each pipe.
The first pipe can fill the pool in 10 hours, so it can fill {{{1/10}}} of the pool in 1 hour.
The second pipe can fill the pool in 6 hours, so it can fill {{{1/6}}} of the pool in 1 hour.
Together, both pipes can fill {{{1/10+1/6 = 4/15}}} of the pool in 1 hour.
Therefore, it will take {{{15/4 = highlight(3.75)}}} hours for both pipes to fill the pool.