If the ratio of boys to girls in a class is 3:1, then the class can be divided into 3+1=4 equal parts, of which 3 parts are boys and 1 part is girls.
Let the total number of parts be 4x (where x is a constant), then the number of boys is 3x and the number of girls is x.
We know that the total number of students in the class is 36, so:
3x + x = 36
Simplifying the left side of the equation, we get:
4x = 36
Dividing both sides by 4, we get:
x = 9
Therefore, the number of girls in the class is x = 9.
Answer: There are 9 girls in the class