It is determined by the number of seats available at the college. Calicut University does not conduct exams properly, and your grades will not be corrected. This means that the student who studies the best in class and the student who did not study for the exam get nearly the same grade. 

The university doesn't even properly correct the papers. It's also evident in newspaper articles about the majority of students failing a university exam. Your semester exams will be held on an irregular basis. That is, if you are in the third semester, you may write for the first semester. 

Furthermore, if you fail at some point in the third semester and all of the other semesters succeed, it will take years for you to pass the exam because the supplementary exam is not given frequently.