On a certain hot summer's day, 321 people used the public swimming pool. The daily prices are $1.75 for children and $2.00 for adults. The receipts for admission totaled $634.25. How many children and how many adults swam at the public pool that day?​

120 children and 388 adults bought tickets for the swimming pool
Explanation:
Create two simultanous equations:
Let c stand for the number of children that bought a ticket, and a stand for the number of adults that bought a ticket, you get your first equation, being
c
+
a
=
508
then, you now create a second equation for the prices of the tickets.
(price of childrens tickets)(number of children that swam)+(price of adults tickets)(number of adults that swam) = total money collected
so:
1.75
c
+
2.25
a
=
1083.00

now we still know, that
a
=
508
−
c

so we can substitute it into the second formula
1.75
c
+
2.25
(
508
−
c
)
=
1083

now its just simple algebra
1.75
c
+
1143
−
2.25
c
=
1083

60
=
0.5
c
so:
c
=
120
now we know, that 120 children went to the swimming pool.
and we still have the formula from before:
a
=
508
−
c
so
a
=
388