Boys account for 2/3 of all students.

Girls account for 1/3 of all students.

The second category:

Boys account for 2/5 of all students.

Girls account for three fifths of all students.

The third category:

Boys account for 3/ 10 of all students.

Girls account for 7/ 10 of all students.

Your question is not easy to understand, so I will write two understandings:

The ratio of boys to girls is (2/3+2/5+3/10): (1/3+3/5+7/10).

Finishing: 4 1: 49

The ratio of boys in the three classes is 20: 12: 9.

The ratio of girls in three classes: 10: 18: 2 1.

I hope my answer is helpful to you. Take it, O(∩_∩)O!