There are 80 children. 45 of them are girls. The amount of boys is equal to:
[tex] 80-45 = 35 [/tex]
That means there are 45 girls and 35 boys.
The ratio of boys to girls is: [tex] 35:45 [/tex]
Simplify:
[tex] 35 \div 5 = 7 \\ 45 \div 5 = 9 \\ \\35:45 \rightarrow 7:9 [/tex]
Your answer is 7:9