The easiest way to find out ratios is to divide the total (in this case, students) by the divider (in this case, the classrooms).
156 ÷ 6 = 26
The ratio of students to classrooms is 26 students per classroom, or 26 : 1.
In this case, you need to figure out how many girls there are first.
156 - 80 = 76
Because you don't want to end up with a decimal, you need to find the GCF.
The factors of 76 are: 1, 2, 4, 19, 38, 76
The factors of 80 are: 1, 2, 4, 5, 8, 10, 16, 20, 40, 80
Your GCF is 4, which is number you divide your total number of boys and total number of girls by.
80 ÷ 4 = 20
76 ÷ 4 = 19
The simplest ratio of boys to girl is 20 boys for every 19 girls, or 20 : 19
