Math paradox lets you cheat your friends
The Setup: First, make yourself a set of "non-transitive dice". These are dice that are completely ungimmicked, but they have a different set of values on each side of the die than you would normally find. All you'll need is 6 dice and some model airplane paint. Paint 2 of the dice completely green, 2 completely red, and 2 completely blue. Next, assign number values as you see here:
Red: 1 4 4 4 4 4
Green: 2 2 2 5 5 5
Blue: 3 3 3 3 3 6
...if you don't want to spend the time to make your own, google "non-transitive dice" and you'll be able to buy some pre-made online. Just make sure they're the same style as the ones we're making here.
The Game: set out one die of each color, and challenge your sucker to pick any dice for a head-to-head "best of ten" challenge. Feel free to let them examine the dice, and freely let him consider which values are most likely to win. Once he picks his die, you pick yours accordingly:
If he picks Red, you pick Green
If he picks Green, you pick Blue
If he picks Blue, you pick Red
In a match of 10 throws, you will almost always win. It sounds crazy, but all three of these non-transitive dice is designed to beat out at least one of the other two. Here are the numbers:
In a face-off between Green and Red, GREEN wins roughly 58% of the time
In a face-off between Blue and Green, BLUE wins roughly 58% of the time
In a face-off between Red and Blue, RED wins a whopping 69% of the time!
Here's the best part of the scam: after you've won a few times, you can completely explain how you're winning, but STILL beat the sucker! Once you've gotten a couple of free drinks, explain exactly how the dice work and which color will beat each other color. Then offer to play one more time to test their understanding... but this time, use 2 dice of each color to play.
Amazingly, when you double the number of dice, the advantages COMPLETELY flip in the other direction! For example:
In a face-off with TWO dice between Green and Red, RED wins roughly 59% of the time
In a face-off with TWO dice between Blue and Green, GREEN wins roughly 59% of the time
In a face-off with TWO dice between Red and Blue, BLUE wins roughly 52% of the time (notice the small margin of victory on this one, and remember it... you might want to go for best of 20 if they pick Red)