Una carta con cualquier número es un truco clásico. Aquí tienes una versión relativamente sencilla que utiliza un par de dados y una propiedad bien conocida de los dados.
Efecto: Spectator selects a card and returns it to the deck. The magician shuffles the deck several times. The magician pulls out a pair of dice and hands them to the spectator, telling them to roll them a few times to see that they are not loaded.
The magician then tells the spectator that they are going to generate a random number. Tell them that you will turn away so you can’t see and you will tell them what to do.
Turn away and have them roll the dice. Have them add the tops of the two dice together. Then they are to pick up either one of the two dice and look at the bottom of that die. Tell them to add that number to their total. Then tell them to roll that single die. Have them add the number from that single roll to the total.
When they have done that turn around and say that they now have a random number that only they know.
Hand them the deck and have them deal the number of cards corresponding to the number they have. Have them turn the last card dealt. It is their card.
Método: Have a card selected and control it to the top. Now maneuver it to the 13th position. I simply do three riffle shuffles adding four cards to the top each time. You could also use an overhand shuffle or any combination.
When they have rolled the dice and added the numbers, turn around and say that they now have a random number that only they know. The number will be between 9 and 19, with 12 and 13 being the most common.
As you say that glance at the two dice, total them and add seven. That is the number they have in their mind. You now know if you have to add or subtract some cards to/from the top of the deck.
Alternatively, look at the two dice. If they total 6 then you are set, because 6 plus 7 equals 13. If they total a number under six then you need to remove cards from the top of the deck equal to 6 minus the total. If they total over six then you need to add to the top of the deck equal to the total minus 6.
If the total is 12 or 13 they can deal the cards right away. Just have them turn over the next card (in the case of 12), or the last card dealt (in the case of 13).
For any other number you can add or subtract cards with tabled cuts or shuffles.