For this question, I would first see what one child is equal toby divide the children by the percentage.
15÷3= 5
Each child is worth 5%. If you know each child is worth 5%, and the total number of students are 100%, then you can divide.
100÷5= 20
There are 20 students in the class. To make sure our answer is right, we can check to see if 3 students are 15 percent.
3÷20= .15×100= 15
So yes, there are 20 students in the class.