Question

if their are 15 girls and 9 boys in art class, the ratio of girls to boys in the class is

Answer 1

The ratio of girls to boys is 5:3

Just divide both numbers by the GCF which is 3. 

Answer 2

Girls : Boys 
15     :   9
(÷3)   :  (÷3) 
 5      :    3

Answer: 5 : 3