MathDB
18 dominoes in 6x6 board (Chile NMO 1991 P3)

Source:

November 20, 2021
Tilingtilescombinatorics

Problem Statement

A board of 6×66\times 6 is totally covered by 1818 dominoes (of 2×12\times 1), that is, there are no overlaps, gaps, and the tiles do not come off the board. Prove that, regardless of the arrangement of the tiles, there is always a line that divides the board into two non-empty parts, and without cutting tiles.