From the picture, you can see the figure can be decomposed into two identical large triangles with area 20, and 4 identical longer ones, that have to cover the remaining area 40, thus 10 each.
16 classes have 25 students each which EQUALS a total of 400 students and 3 classes which each have 100 students each which EQUALS a total of 300 and 1 class has a total of 300 students and the total number of students is 1000
