The sum of two dice rolls is 6. What is the probability that the number 3 appeared at least once?
The possible outcomes are:
a 1 and a 5
a 2 and a 4
a 3 and a 3
Of these 3 possible outcomes, there is 1 where the number three appears at least once.
And so the probability that the number three appeared at least once = 1/3