China 2010 quiz5 Problem 2
Source:
September 13, 2010
combinatorics unsolvedcombinatorics
Problem Statement
In a football league, there are teams. Each team has a homecourt jersey and a road jersey with different color. When two teams play, the home team always wear homecourt jersey and the road team wear their homecourt jersey if the color is different from the home team's homecourt jersey, or otherwise the road team shall wear their road jersey. It is required that in any two games with 4 different teams, the 4 teams' jerseys have at least 3 different color. Find the least number of color that the teams' jerseys may use.