Question: If there are 85 students in a statistics class and we assume that there are 365 days in a
year, what is the probability that at least two students in the class have the same birthday
(assuming birthdays are distributed independently)?
How close is that to certainty? Well suppose certainty is represented by a metre stick — 0cm being impossible and 100cm being certainty. How far away from the 100cm mark would we be? We would be less than a human hair’s width from the 100cm mark!!
A more interesting number than 85 is 87 people because 87 people in a room is the number of people needed to give a 0.5 (i.e. a flip of a coin) chance that at least THREE people share the same birthday. 🙂