In a classroom, what is the probability that 2 students will celebrate their birthdays on the same day? With 365 days a year, around thirty students in the class, we say to ourselves that it must be weak … Think again! It only takes 23 people for there to be more than a 50% chance that 2 people will have their birthday on the same day. From 41 people, the probability is more than 90%! This is what this simple application will allow you to experiment. Try with dates of birth, car numbers etc …