Math in the Middle Institute Partnership


Date of this Version



In partial fulfillment of the requirements for the Master of Arts in Teaching with a Specialization in the Teaching of Middle Level Mathematics in the Department of Mathematics. David Fowler, Advisor July 2007


Question, how many people would you need in a group in order for there to be a 50-50 chance that at least two people will share a birthday? Answer, 23 people. But how can this be? There are 365 days in a year and half of that would be 182, so why wouldn’t you need at least 182 people to have a 50-50 chance? Strangely enough the answer to this question is only 23 people are necessary to have a 50% chance at least two people in the group will share a birthday. This situation, where the answer is counter intuitive, is called a paradox, making the official name for this probability problem, the Birthday Paradox.