1. there are 3500 students, and 2000 of them are girls, which means:

3500-2000 = 1500

there are 1500 boys in that school.

a. the ratio of girls to boys is

2000 : 1500, divide both by 500

4 : 3

b. the ratio of girls to all students is

2000 : 3500, divide by 500

4 : 7

the ratio of boys to all students is

1500 : 3500, divide by 500

3 : 7

2. the employees that is working on marketing are

1200-(160+240) = 1200-400 = 800

a. ratio of publishing dept to all employees is

240 : 1200, divide both by 240

1 : 5

b. ratio of admin dept to all employees is

160 : 1200, divide both by 80

2 : 15

c. ratio of marketing dept to all employees is

800 : 1200, divide both by 400

2 : 3