I'm confused. I have questions in my book about numeric probability like this: "A painter numbers copies of his paintings with a 4 digit number and makes enough copies to use all the possible 4-digit numbers. If you buy a painting, what is the probability of getting painting #5142?" In the answer key, it is 1/10,000 (10x10x10x10). I totally don't get this because if you have 4 digits to work with, you can only go up to 9. 10 is a 2-digit number. please explain how they are getting this answer.