From the information available, 4 sandwiches are EQUALLY shared by 5 people.
If for example the sandwiches were to be shared among 2 persons, then we would have;

In the same manner if 4 sandwiches were to be shared equally among 5 people, then we would have;

ANSWER:
Each student would get 4/5 of a sandwich. This is because the total number of sandwiches is less than the total number of persons sharing. That is the reason why each peron cannot get a whole sandwich to himself/herself. Each person can only get four-fifths of a sandwich.