13. You roll two (fair) dice. a. What is the probability that at least one of the dice has rolled a 4? b. You are told the sum is X. Conditioned on the value of X, for X z 2, 3, . . . , 12, What is the probability that at least one of the dice has rolled a 4 now? (3. Compute the probability that 'the sum is 10' conditioned on 'at least one of the dice has rolled a 4