There are 156 students in 6 different classrooms. what is the ratio of students that classrooms? if there are 80 boys what is the ratio of boys to girls?

156-80=numb of girls 
numb of girls: 76

Ratio of boys to girls=80:76
=20:19

Ratio of students in classrooms= 156:6
=26:1

(assuming that each classroom has the same number of students)

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