Happy Birthday, guys.
Now Solus, what you're asking is called the Birthday Paradox
Now what are the odds two folks would have the same birthday? Just a tiny tad under 1 in 365, actually.
With a group of only 23 people there's a 50% chance of at least two having the same birthday. The odds approach 100% with only 70 people. This type of probability is important to know for a number of applications. For example, if a brand of car has 10,000 different key combinations, then in a parking lot of 1,000 cars, how many will use the same key? Or given 4 digit pin numbers, how many of us have the same pin?