In the fairest school 70% are below 16 years old 1/3 are teachers which is equals to = 21 Let’s start solving: => 1/3 of 100% => 100 / 3 = 33.33% thus 33.33% = 21 => 21 x 3 = 63, is the total number of people in the school. Let’s try solving the number of people below 16 years old Have you notice that you are asking for a 70% of students but there are already 33.33% of teacher. Thus your given problem is not right already. => 100% - 33.33% = 66.67% that’s the only remaining percentage and not 70% => 63 * .6667 = 42.0021 Thus, there are around 42 people who are 16 years old younger.