Suppose that we roll two fair 6-sided dice. What is the probability that the two numbers rolled sum to 4?

There are 3 ways to roll a sum of 4: 3 on the first die and 1 on the second die, 2 on the first die and 2 on the second die, and 1 on the first die and 3 on the second die. There are 36 total possibilities, so the probability is .