in a chemistry class, the ratio of girls to boys is 2 to 1. if there are 30 students in the class how many girls are there

Firstly, we can simplify the ratio of boys to girls to
1
:
2
.
Then, to find out how many students each ratio represents, we add up
1 and 2 to get 3
(1+2=3)
By dividing 3
by the number of students, we can find how many students ONE ratio represents:
24 3=8

So ONE ratio is equal to 8
boys. Since our simplified ratio of boys to girls is
1:2
already, we do not have to do further multiplying - the number of boys is simply 8.
For the girls, simply multiply 2 by 8 to get 16

Check: 8 boys + 18 girls = 24students