If it’s one day till Christmas, it’s Christmas Eve (one Eve).But it’s nine more days, so add nine more Eves, for a total of ten.
Something similar we called “fencepost errors” in school. Suppose you need to bjuild a fence 30 feet long. Each piece of fencing material is 5 feet long. How many fenceposts do you need? (Hint: 5 * 6 = 30.)
The Great Penguin will bring you a present if your belief in him is sincere.