You've got a stack of cards numbered 0 through 5. What is the probability that you would pull two cards that total 3. If you pull a zero initially, there's only one card you can pull(the 3) to total 3. If you pull a 1, then you have to pull a 2. If you pull a 2, then you have to pull a 1. If you pull a 3, you have to pull a zero. So there are only four combinations of cards that are going to get us to our total of 3. How many total combinations of cards are available? Well, if you pull that zero, you can pull 1,2,3,4,5; there are five cards you can pull. If you pull a 1, you can pull a zero,2,3,4,5. So, you have six combinations of five cards that are total possible pulls; of those thirty, four will work. So, 4 out of those possible 30 or 2 out of 13 is the ratio, or as a decimal it is .133.