Each of n guests at a party wears a hat of one of three colours. A guest is said to be
lucky if at least two of its friends in the party wear differently coloured hats. Find all values
of n for which it is always possible to choose a guest and to change its hat to hat of one
of the remaining two colours such that the total number of lucky guests will not be decreased.
Correct Solutions by,
- Toshihiro Shimizu Kawasaki, Japan
- Serdar Hojayev Dashoguz, Turkmenistan
- Mehmet Sarak İstanbul Bahçeşehir Fen ve Teknoloji Lisesi
- Mustafa Burak Topal İstanbul
Solution: http://www.fen.bilkent.edu.tr/~cvmath/Problem/2210a.pdf