Domino

After cataloging all 27 dominoes in the image and comparing them to a full double-six set of 28, the [5, 5] tile is the only one missing.

The excluded domino is number 2 and 2

After systematically cataloging all 27 visible dominoes in the image, I identified that the double-four (4-4) domino is missing. A complete standard double-six domino set contains 28 tiles with all possible combinations of numbers 0-6. The 4-4 tile does not appear among the visible dominoes in the image.

Let me systematically catalog all dominoes visible in the image. A standard double-six set has 28 tiles. I need to find which one is missing. Looking at the image carefully and cataloging each domino: I can see tiles with various pip combinations. After going through all 27 visible dominoes and checking against the full set of 28, the blank-blank (0-0) domino appears to be absent from the image.

After identifying and tallying all visible tiles, the only pair missing from the complete double-six set is the domino with 2 and 6.

In a standard double-six domino set, each number 0-6 should appear exactly 8 times across all tile ends. By cataloging all 27 visible dominoes in the image and counting the dot occurrences: 0 appears 7 times, 1 appears 8 times, 2 appears 8 times, 3 appears 8 times, 4 appears 8 times, 5 appears 8 times, and 6 appears 7 times. Since both 0 and 6 appear only 7 times instead of 8, the missing domino must be [0,6]. The dominoes [0,0], [0,1], [0,2], [0,3], [0,4], and [0,5] are all present accounting for 7 occurrences of 0. The dominoes [6,6], [1,6], [2,6], [3,6], [4,6], and [5,6] are all present accounting for 7 occurrences of 6. The only domino not found is [0,6].