20 math and 11 physics problems
Source: Junior Turkish Mathematical Olympiad 2011 P4
July 2, 2012
graph theorycombinatorics proposedcombinatorics
Problem Statement
Each student chooses math problem and physics problem among math problems and physics problems. No same pair of problem is selected by two students. And at least one of the problems selected by any student is selected by at most one other student. At most how many students are there?