Two fair dice are thrown. What is the probability that the difference of the numbers is 2?

Explanation

1. 01

   List the 36 equally likely ordered pairs $(a, b)$.

2. 02

   The difference is 2 for (1, 3), (2, 4), (3, 5), (4, 6) and the same four reversed: 8 pairs, so $\frac{8}{36} = \frac{2}{9}$.