The ratio of boy to girls in a class is 3 : 2. There are 15 boys in the class. How many total boys and girls are in the class?

A) 15

B) 23

C) 25

D) 35

First, let's see what we are told:

1. The ratio of boys to girls is 3:2. Turn that into an equation

2b=3g 2b=3g

2. If two girls are added, the number will be equal

b=g+2 b=g+2

Now, substitute the second equation into the first:

2 (g+2) = 3g 2 (g+2) = 3g

multiply

2g+4=3g 2g+4=3g

subtract 2g

4=g 4=g

So there are 4 girls and, thus 6 boys

3:2 = 15:10 (3x5 = 15 boys; 2x5 = 10 girls)

15+10=25 total boys and girls

answer C) 25