probability igcse

Question

two fair dice are rolled the scores on the two dice are added to give the total.Given that the score on at least one of the dice is 2 calculate probability that total is 5

Answer 1

There are 11 distinct rolls of equal probability such that at least one of the dice is a 2. That is the sample space. Of those rolls, there are 2 distinct rolls such that the sum = 5. P(sum of 5 | at least one die is 2) = 2/11