betterexplained.com

woGJo TIL in a group of 23 randomly selected people there is a 50% chance that at least two of them have the same birthday
BrOnb TIL of the Pareto Principle (also known as the 80/20 rule) which states that for many events roughly 80% of the effects come from 20% of the causes.(reuploaded with a working link)
JYDYB TIL about The Birthday Paradox. In a room of just 23 people, there’s a 50-50 chance of at least two people having the same birthday. In a room of 75, there’s a 99.9% chance of at least two people matching.