Arrange the 28 pieces of a standard domino (0-0 to 6-6) in the board shown, so that equal spot numbers occur in groups of four, forming squares. Fourteen squares should result, each containing four equal spot numbers.

            +---+---+       +---+---+
            |   |   |       |   |   |
            +---+---+---+---+---+---+---+---+
            |   |   |   |   |   |   |   |   |
            +---+---+---+---+---+---+---+---+
            |   |   |   |   |   |   |   |   |
            +---+---+---+---+---+---+---+---+
            |   |   |   |   |   |   |   |   |
            +---+---+---+---+---+---+---+---+
            |   |   |   |   |   |   |   |   |
            +---+---+---+---+---+---+---+---+
            |   |   |   |   |   |   |   |   |
            +---+---+---+---+---+---+---+---+
            |   |   |   |   |   |   |   |   |
            +---+---+---+---+---+---+---+---+
            |   |   |       |   |   |
            +---+---+       +---+---+

(In reply to Pencil and paper solution. by Charlie)

There are bold horizontal lines in the diagram to delineate the dominoes in the previous post, but they don't look bold.

So:

            +---+---+       +---+---+
            | 0   0 |       | 2   2 |
            +---+---+---+---+---+---+---+---+
            | 0 | 0   4 | 4   2 | 2   6 | 6 |
            +   +---+---+---+---+---+---+   +
            | 5 | 5   4 | 4   1 | 1   6 | 6 |
            +---+---+---+---+---+---+---+---+
            | 5 | 5   3 | 3   1 | 1   5 | 5 |
            +   +---+---+---+---+---+---+   +
            | 2 | 2   3 | 3   6 | 6   5 | 5 |
            +---+---+---+---+---+---+---+---+
            | 2 | 2   0 | 0   6 | 6   4 | 4 |
            +   +---+---+---+---+---+---+   +
            | 1 | 1   0 | 0   3 | 3   4 | 4 |
            +---+---+---+---+---+---+---+---+
            | 1   1 |       | 3   3 |
            +---+---+       +---+---+

Posted by Charlie on 2008-08-15 12:22:27