There are 30 students in a class for every 3 girls in the class there are 2 boys how many girls are in the class?

Answer 1

Okay, first you need to show the girls and boys in the class.

G + B = 30

Next you need to relate the Girls to Boys. This is hard to see at first glance but consider this. Girls and boys are equal. In a set of girls each girl is 1/3 of the set. In a set of boys each boy is 1/2 of the set. So we can look at equal girls and boys like this.

G/3 = B/2

Now, lets fix this equations a little bit by multiplying by 3.

G = 3B/2

I can substitute this into the first equation (using 3B/2 for G)

3B/2 + B = 30

5B/2 = 30

5B = 60

B = 12

We can now bo back to the first equations with B=12

G + 12 = 30

G = 18

And you ALWAYS ALWAYS check that this fits the other equation

18/3 = 12/2

6 = 6. Right.