If 3 people enter a room, what is the probability no two have the same birthday month?

If 3 people enter a room, what is the probability no two have the same birthday month?

Approach: Sequential probability calculation.

55/72. (12/12) * (11/12) * (10/12) = 110/144 = 55/72.

Follow-up: At what number of people is the probability 0?

Key concepts: pigeonhole principle.