Refer to Exercise 1. In this exercise, another method is used for finding the probability that at least one of two unrelated strangers shares your birth month.
a. What is the probability that the first stranger shares your birth month?

b. What is the probability that the second stranger shares your birth month?

c. What is the probability that both of them share your birth month?

d. Use Rule 2a ("either A or B or both") to find the probability that at least one of the strangers shares your birth month.

Exercise 1
In Example 2, we found the probability that both of two unrelated strangers share your birth month. In this exercise, we find the probability that at least one of the two strangers shares your birth month. Assume that all 12 months are equally likely.
a. What is the probability that the first stranger does not share your birth month?

b. What is the probability that the second stranger does not share your birth month?

c. What is the probability that neither of them shares your birth month?

d. Use the result from part (c) to find the probability that at least one of them shares your birth month.

Example 2
Probability That Two Strangers Both Share Your Birth Month Assuming that birth months are equally likely, what is the probability that the next two unrelated strangers you meet both share your birth month? Because the strangers are unrelated, we assume independence between the two events that have to do with them sharing your birth month. Define

Event A = first stranger shares your birth month: P(A) = 1/12.

Event B = second stranger shares your birth month: P(B) = 1/12.