Throughout this trick, Aces are 1, 2s are 2, 3s are 3, …, 10s are 10, Jacks are 11, Queens are 12, and Kings are 13.
Place the top card of the deck face up on the table. Look at the number of the card, and starting with that number deal more cards face up on top as you count to 15. For example, if the card is a 9 then you would place six more cards face up on top as you count 10, 11, 12, 13, 14, 15. Once you’ve finished, turn the pile face down.
Form a new pile by repeating the procedure: if the first card you turn over is a Jack (which counts as 11) you’d place four more cards face up on top of the Jack as you count 12, 13, 14, 15. Once you’re done, turn the pile face down.
Continue with this procedure, forming separate piles, until you’ve used up all your cards. The piles may come out evenly; if you don’t have enough cards to finish a pile, then pick up the incomplete pile and hold it in your hand.
Now have The Volunteer choose any three piles; leave those piles alone, and pick up the rest of the piles, adding them to any that are in your hand.
Count out 4 cards from your hand, and give them to The Volunteer. Have The Volunteer turn over the top card on two of the piles, and give that number of cards to The Volunteer as well. For example, if The Volunteer turns over an Ace (1) and a Queen (12) then you’d give The Volunteer 1+12=13 additional cards from your hand.
Now for the magic: Turn over the top card on the remaining pile. Voilá — it equals the number of cards left in your hand!
Note: There are some variations on this. You can count up to 16 instead of 15 when you make piles; in this case you initially give The Volunteer 1 instead of 4 cards. Or you could only count to 14 or 13 and then you’d have to give The Volunteer 7 or 10 cards initially. The smaller the number, the more piles you’ll (probably) end up with to choose from, which can appear more impressive.
Anyone see how it works?
This is a variation of a card trick posted at Card Trick Central.