Problem

Source: St. Peterwbug MO 2001, 11th grade, P7

Tags: combinatorics, Tiling, Coloring, Rectangles, dominos



Rectangles $1\times20$, $1\times 19$, ..., $1\times 1$ were cut out of $20\times20$ table. Prove that the maximal amount of $1\times2$ dominos can be cut from the table is 85 Proposed by S. Berlov