03 May '10 17:36

If a domino piece is exactly the size of two squares of the chessboard, it would take 32 domino pieces to cover the 64 squares.

Each domino can be either horizontal (long edges parallel to the ranks) or vertical (long edges parallel to the files).

Prove that the number of horizontal dominoes must be even.

Each domino can be either horizontal (long edges parallel to the ranks) or vertical (long edges parallel to the files).

Prove that the number of horizontal dominoes must be even.