Domino

By systematically checking all 28 possible dominoes in a standard double-six set, the domino [4, 4] (double-four) is not present in the image. All other dominoes from [0,0] through [6,6] can be identified among the 27 tiles shown.

The image contains 27 dominoes. A standard double-six domino set has 28 unique tiles. By examining the image, we can identify the dominoes present and compare them to the complete set. Upon inspection, we find that the domino [3, 3] is missing.

The excluded domino is number 6 and 6

After analyzing the image and counting occurrences of each number across all halves of the 27 dominoes, numbers 4 and 6 each appear 7 times, while all other numbers (0 through 3 and 5) appear 8 times, indicating the missing domino is [4,6].

In a standard double-six set, each number from 0 to 6 appears 8 times as a half (since 28 tiles × 2 halves = 56 sides, and 56 / 7 numbers = 8). The missing domino is the only one not present. Counting the occurrences of 0 dots (blank sides) in the image shows 6 occurrences. Since the full set has 8, the missing domino must be [0, 0] (contributing 2 extra 0s in the full set, so 8 - 2 = 6 in the image). All other numbers appear 7 or 8 times, confirming [0, 0] is the missing tile.

A standard double-six domino set contains 28 unique tiles. By carefully examining the 27 dominoes shown in the image, I identified all doubles present: [0,0], [1,1], [2,2], [3,3], [4,4], and [5,5]. The double [6,6] (which would show two squares each containing six dots arranged in two columns of three) is not visible anywhere in the image. All other dominoes from the standard set can be accounted for in the arrangement, including [0,6], [1,6], [2,6], [3,6], [4,6], and [5,6] which appear in various positions. Since exactly one domino is missing and [6,6] is the only one not present, the excluded domino is [6,6].