8

Part of 2003 Junior Tuymaada Olympiad

Problems(1)

2 rooms, everyone has even number of acquaintances in his room

Source: Tuymaada Junior 2003 p8

A few people came to the party. Prove that they can be placed in two rooms so that each of them has in their own room an even number of acquaintances. (One of the rooms can be left empty.)