nice easy problem
Source: Ukrainian TST 2007 problem 7
September 19, 2007
graph theorycombinatorics proposedcombinatorics
Problem Statement
There are 25 people. Every two of them are use some language to speak between. They use only one language even if they both know another one. Among every three of them there is one who speaking with two other on the same language. Prove that there exist one who speaking with 10 other on the same language.