Percentage of students that are girls in the class = 60% Number of girls in the class = 18 Let us assume the total number of students in the class = x Then 60% * x = 18 (60/100) * x = 18 6x/10 = 18 6x = 18 * 10 6x = 180 x = 180/6 = 30 So the total number of students in the class is 30. Number of boys in the class = 30 - 18 = 12 So there are 12 boys in the class. I hope the procedure is simple enough for you to understand.