(a) The sample space is the set of all ordered pairs of birth days (that is if the two people are distinguishable) or of all sets of two birth days (if the people are not distinguishable the order of the dates is not relevant)

(b) Suppose the people are distinguishable, the first can gave any of birthdays, and independently the second can have any of the birthdays. All of these are equally likely so the number of possible pairs of birthdays is , and as these are all equally likely the probability of any one is .

CB