If you bought a pack of 0-6 dominoes, and they came in a bag, and if you wanted to check if you had a full set, you could count the number of dominoes with a particular number on one side, and then see if it adds up to 7, because there are 7 sets of each number. With this method, you can find out exactly what domino you are missing. For example, if you are counting for the number 3, and there are 6 dominoes, and 3 with 0, 1, 2, 3, 5, and 6, then you know that the 3/4 domino is missing. This is a more efficient, and quicker method than counting all the dominoes individually, but if you chose to do that, then you would know if there is a full set by having 28 dominoes in total.

In a set of 0-9 dominoes, you could use the same method mentioned above to find out if you have a full set. However, if you choose to count the dominoes individually, you would know if you are correct by having 55 dominoes in total.