Explanation:
the ratio of the pool lengths is 3/5.
that means for every 3 meters of length on Shantel's pool, there are 5 meters of length on Juan's pool.
it the other way around : to get to the size of Shantel's pool, every 5 meters of length on Juan's pool are converted to 3 meters.
x = length of Juan's pool
x × 3/5 = 30
3x = 150
x = 50 meters
you see the relationship ?
3/5 = 30/50 = 300/500 = ...
but it is true for any factor
3/5 = 15/25 = 24/40 = 6/10 = ...
once you see the factor for one part of the ratio, you know there is the same factor for the other part (or parts) of the ratio. otherwise the ratio would not stay the same and keep the relationship.