Question 811619
This ratio can be shown as 3/5 also. (6/10=3/5)
Now, since there are 30 girls, you make this into a set of fractions that equal each other.

3/5 = 30/x
Now, 3*10 = 30, so you can multiply by 10 in the denominator as well. 5*10 = 50.
So there are 50 boys in the geometry class.