If there's 32 boys, which is 4 times the amount you start with, you have to apply that to the number of girls as well since for every 8 boys, there is 2 girls.
There are several ways to do this but one of them is to find how many groups of 8 boys are in 32. To do this we divide 32 by 8 which equals 4. We then multiply 2 by 4 which is 8.
