You start by making an equation:
3x+5x=120
Then combine like terms
8x=120
Divide 8 by both sides
x=15
Now that we have that we can figure out how many children and adults there are
Children: 3x15=45 children
Adults: 5x15=75 adults
Also, you can type this in your calculator for a faster method
Children : 120 x(3/8) =45
because eight is the sum of the ratio 5+3
And Adults : 120 x(5/8)=75
So the answer to your question is 45 children.
Hope this helps!!!
