Hello!
If there are 32 people in total in the class, and 20 of them are girls, that means there are 12 boys in the class
so the ratio of boys to girls is 12:20
to get simplest form, divide by the greatest common factor. which in this case, is 4.
12 / 4 = 3
20 / 4 = 5
your final answer is: boys:girls, 3:5
I hope this helps, and have a nice day!