There are at least 120 students [2017 Moldova TST, D2, P4]
Source: 2017 Moldova TST, Day 2, Problem 4
March 19, 2017
combinatorics
Problem Statement
At a summer school there are courses. Each participant was a student in at least one course, and each course was taken by exactly students. It is known that for each courses there were at most students who took them both. Prove that at least students participated at this summer school.