There are 5 cards. Lets call them 1,2,3,4, and 5.
Player 1 sends the duel to Player 2 knowing what the cards are.
Player 2 picks a card. Any card. Let's say 3.
The duel goes back to player 1.
If player 1 chooses 3 he wins 4 times the amount of points he wagered. If not player 2 wins the amount of wagered points.
The maximum for a wager is 5 points.
Comprohenda?