Answer:
352 children
Step-by-step explanation:
Solve algebraically using a system of equations
Assign variables
let "a" be the number of adults
let "c" be the number of children    <-- We want to find this
a + c = 541             Equation for number of people
2.25a + 1.75c = 1041.25           Equation for money
<u>Rearrange the equation for people</u>. Isolate the variable you don't want to find.
a = 541 - c
<u>Substitute</u> "541 - c", replacing "a", in the equation for money
2.25a + 1.75c = 1041.25               
2.25(541 - c) + 1.75c = 1041.25               Distribute over brackets
1217.25 - 2.25c + 1.75c = 1041.25               Collect like terms
1217.25 - 0.5c = 1041.25                   Simplified equation
<u>Start isolating "c".</u> Move anything that's not "c" to the right side. Move numbers in reverse BEDMAS order. That means we will add/subtract before dividng/multiplying. When moving a number, do its reverse operation to the entire equation.
1217.25 - 0.5c = 1041.25      Do the reverse of positive 1217.25
1217.25 - 1217.25 - 0.5c = 1041.25 - 1217.25    Subtract 1217.25 on both sides  
-0.5c = -176               Do the reverse of multiplying by -0.5
-0.5c/-0.5 = -176/-0.5               Divide both sides by -0.5
c = 352                Number of children
Therefore, there were 352 children in the pool.