In a school, the ratio of boys to girls is 6 : 5 and the ratio of girls to teachers is 7 : 2. The ratio of students to teachers is:

Let the number of teachers be x.

? girls : teachers = 7 : 2,

Number of girls = (7/2) × x = 3.5x

Now, since ratio of boys : girls = 6 : 5

Number of boys = (6/5) × 3.5x = 4.2x

Number of all students = number of boys + number of girls

= 4.2x + 3.5x = 7.7x

∴ Ratio of student: teachers = 7.7x : x = 77 : 10

Hence, the ratio of all students and teachers is 77 : 10