Hi! I'm happy to help!
To solve for this, we need to understand what a ratio is. A ratio is a comparison between two things. (in numbers) In this case, between pools and hours:
pools:hours
A fraction is also a ratio, in this case we have 2/5, which also compares pools to hours, so we can turn this into a more proper ratio form:
2 pools: 5 hours
2:5
So, our ratio of pools to hours is 2:5.
I hope this was helpful, keep learning! :D