Quick: in your own mind, imagine you're at a party with 35-40 people. What do you think are the odds that two people will share the exact same birthday?

Remember, we're looking at about 40 people in the room, and there's 365 days in the year, so would it be...

(a) 0-25%

(b) 25%-50%

(c) 50%-75%

(d) 75%-85%

(e) Over 85%

Most people tend to pick (a) or (b), and then occasional smartass will go as high as (d)... but the shocking truth is that with 40 people in the room, the answer is (e), over 85%!

This is a case where the human mind just isn't wired correctly to grasp true probability. Most of us figure "okay, there's about 40 people and about 365 days... so the answer must be about 40/365... which is about 10%." However, the true math is far more complex. To learn more about it, check out this Wikipedia article on the paradox

Here's a few numbers to keep in mind when you're trying to decide if the time is right for you to play this trick:

The odds are 50% you'll get a match with only 23 people in the room

The odds are 80% you'll get a match with only 35 people in the room

The odds are 90% you'll get a match with only 42 people in the room

The odds are 99% you'll get a match with only 57 people in the room (wow!)