Tilings

If we remove two opposite corners of an 8 × 8 8\times8 chessboard, is it possible to tile the resulting figure with 31 31 dominoes?

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2 solutions

Brian Lie
Jun 26, 2019

Our chessboard would not be a chessboard if its cells were not colored black and white alternatingly. As it turns out, this coloring is crucial in answering the question at hand.

Notice that, regardless of where it is placed, a domino will cover one black and one white square of the board. Therefore, 31 31 dominoes will cover 31 31 black squares and 31 31 white squares. However, the board has 32 32 black squares and 30 30 white squares in all, so a tiling does not exist.

Just brilliant!

Charles Hurtado - 1 year, 10 months ago

you never said how big the dominoes were

Jad Essadki - 1 year, 9 months ago

We know the diagonal of the chess board is all the same colour. So we removed 2 of the same colours by removing the opposite corners, so now there is 30 of one colour and 32 of the other. A domino covers one of each colour and so after we using 30 dominos we have two of one colour left over which cannot be covered by a single domino ( because it covers 1 of each colour not two of the same).

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