If the ratio of girls to boys is 3:7,
then: 3/10 of the class are girls and 7/10 of the class is boys
Note: 3+7 = 10
If the class has a total of 50 students we can find the number of boys by doing this:
(total number of kids) x (fraction of the kids that are boys) = # of boys
50 x (7/10) = 35
There are 35 boys in the class.