Answer:
2:1
2:5
4:3
Explanation:
In these examples the comparison words "per", "to", "for every" is the colon.
Then just put the numbers in the same order they are in in the problem
1. Two cookies per student. __:__
Means 2 cookies per 1 student
We're writing the ratio
cookies:students
2:1
2. The odds of the horse winning the race are 2 to 5. __:__
The "to" is the colon
2:5
3. Colorado State University, there are 4 female students for every 3 male students. __:__
We are comparing
female:male
4:3