In Happy Birthday
, the question was if there are N people in a room, what is the probability that there are at least two people in the room who share a birthday?
What if instead exactly two was required? If there are N people in a room, what is the probability that there are exactly two people in the room who share a birthday?
(Note: Assume leap year doesn't exist, and the birthdays are randomly distributed throughout the year.)
(In reply to thoughts
by Bob Smith)
Bob, I disagree. You have to take into account that also the first two
people can heva the same birtday. Just multiplying your solution by n/2
(n position to insert the person sharing a birthday with another,
divided by two because the two can be interchanged).