• ARTICLES
SEARCH

How-To Geek

GEEK TRIVIA

In Your Average School Class There Is A 50% Chance Two People Share What?
Great-Great-Great Cousins
Ear Wax Type
A Birthday
Blood Type


Answer: A Birthday

In the field of probability theory, there is a problem known as the Birthday Paradox concerning the probability that in a selection of N randomly chosen people, some of them will share a birthday. This probability reaches 100% once you reach a sample size of 367 (to account for the 366 potential days, including Feb. 29, +1).

What’s fascinating, however is how quickly the probability of climbs. In a group of 23 people, around the size of your average primary or secondary classroom, the chances of two people sharing a birthday has already climbed to 50%. To get to 99%, you’d just need to gather two classrooms together. In a group of 57 people there is a 99% chance there is a common birthday. The change between 57 and 367 people is a hundredth of a percent per person added to the pool.

While this might seem like something of a mathematical parlour trick, the math behind the Birthday Paradox has actually been successfully employed as a well known cryptographic attack, the Birthday Attack, which uses probabilistic modeling to reduce the complexity of cracking encryption hash functions.

Get Free Articles in Your Inbox!

Join 134,000 newsletter readers

Email:

Go check your email!