Final answer:
275 children and 138 adults swam at the public pool that day.
Step-by-step explanation:
Let's assume that the number of children who swam is x, and the number of adults who swam is y.
The total number of people who swam is 413, so we have the equation x + y = 413.
The total amount of money collected from children is $1.25x, and the total amount of money collected from adults is $2.00y. The total amount collected is $684.25, so we have the equation 1.25x + 2.00y = 684.25.
Solving these two equations simultaneously will give us the values of x and y.
Using substitution or elimination method, we find that x = 275 and y = 138.
Therefore, there were 275 children and 138 adults who swam at the public pool that day.