1998 hexagons, 666 don't share a vertex (Ukraine 1998 Grade 8 P2)
Source:
June 3, 2021
combinatoricsgeometrycombinatorial geometry
Problem Statement
The plane is partitioned into congruent regular hexagons. Of these hexagons, some are marked. Show that one can select of the marked hexagons in such a way that no two of them share a vertex.