Domino

A standard double-six set has 28 unique tiles. The image shows 27 tiles. The included tiles are: [1, 2], [1, 0], [0, 6], [2, 6], [4, 6], [2, 0], [2, 3], [3, 6], [1, 6], [1, 1], [6, 0], [6, 6], [0, 3], [1, 3], [1, 4], [2, 2], [3, 3], [3, 4], [4, 4], [4, 5], [5, 5], [0, 1], [0, 0], [5, 6], [2, 4], [3, 5], [5, 2]. The missing tile, representing the only remaining pair from 0 to 6, is the [0, 5] (or [5, 0]) tile.

The excluded domino is number 0 and 0

I identified all other 27 unique domino pairs from 0–6 in the image; the only pair not present is the domino with 2 and 4 pips, so [2,4] is missing.

The excluded domino is number 5 and 3

By systematically checking all 28 possible dominoes in a standard double-six set, I identified 27 dominoes in the image. The missing domino is [2, 3], which represents a tile with 2 dots on one end and 3 dots on the other end.

In a standard double-six set, the domino (0,0) is the only one with two 0s. Counting the number of sides with 0 dots in the image, there are 6 sides (from dominoes (0,1) to (0,6)), whereas the standard set has 8 sides with 0 dots (2 from (0,0) and 1 from each of the other 6 dominoes with 0). The missing domino must account for the 2 missing 0s, which corresponds to (0,0).