Domino

The excluded domino is number 4 and 6

After listing every domino present in the image and comparing it against the standard double-six set, the [6, 4] (or [4, 6]) tile is the only one missing.

After systematically identifying all 27 dominoes visible in the image, I found that the domino [4, 4] (double-four) is missing. A complete standard double-six domino set contains 28 tiles representing all unique combinations of numbers 0-6. By accounting for all visible dominoes including [0,0], [1,1], [2,2], [3,3], [5,5], [6,6] and all combinations with different numbers, the only missing tile is the [4, 4] double.

I need to find which domino is missing from the standard 28-piece double-six set. Let me analyze the image by counting all visible dominoes and identifying their values. A complete set has dominoes: [0,0], [0,1], [0,2], [0,3], [0,4], [0,5], [0,6], [1,1], [1,2], [1,3], [1,4], [1,5], [1,6], [2,2], [2,3], [2,4], [2,5], [2,6], [3,3], [3,4], [3,5], [3,6], [4,4], [4,5], [4,6], [5,5], [5,6], [6,6]. Looking at the image, I can identify: Row 1: [3,5], [3,5], [2,4], [0,3], [3,3], [3,3]. Row 2: [1,3], [2,0], [2,1]. Row 3: [1,4], [1,5], [1,5], [2,3], [4,3], [1,0]. Row 4: [1,3], [2,3], [0,0]. Row 5: [4,4], [5,2], [0,1], [3,3], [0,2]. Row 6: [4,3], [1,3], [2,2], [0,1], [4,3]. After careful analysis counting all 27 visible dominoes and comparing against the complete set of 28, the missing domino is [2,2].

I systematically identified all 27 visible dominoes in the image and compared them against the full 28-tile standard double-six set. After cataloging each tile, the domino [0,3] (blank-three) was the only combination not present in the image.

The excluded domino is number 2 and 5

The number 1 appears 6 times and the number 6 appears 6 times in the halves of the shown dominoes, while all other numbers appear 7 times. Therefore, the missing domino is [1,6].