Start by introducing three dice: one red, one green, and one blue. You show how the sum of all sides of each die add up to 21, just like regular dice, but not all the numbers from one to six are on each of the dice.
The game is played by rolling one of the dice ten times and totaling the score, so the challenge is to pick the right color. And to be fair, you even let them choose first before choosing your own.
Ten rolls of the dice later, you've won the game and taken all of their money!*
The secret is knowing which color of dice to choose based on an easy to learn delta pattern. Choose the right color, and you'll have a dramatic statistical advantage that will enable you to win most of the time.
But there's a twist! You explain the secret to winning and offer to play the game with twice the dice, claiming that this will double their odds of winning.
Even though they know the secret and have a second identical die to play with, you're able to keep the odds in their favor and have them lose most of the time! Because there's a second secret you didn't share with them. >:)
These special "Delta Dice" are very hard to find due to their non-transitive nature, but we've got them in stock right now.
*Maybe don't take all of your friends' money.