Shuffle a deck of cards. Place the top card face up on the table and look at its number (Jacks, Queens, and Kings all equal 10.) Put enough cards on top of the card to make the total 10. For example if a 4 is showing, then you would put 6 more cards on top of it. Put the cards on so that all are face up. Keep making piles like this, until the deck is used up. If there are remaining cards that do not exactly equal 10, hold onto them.
Ask someone in the audience to choose three pile
, each with three or more cards in it, and flip them face down. Pick up the rest of the piles. Count 19 cards from those in your hand, and place them to the side, as they are unnecessary for the rest of the trick.
Ask the volunteer to flip the top card of any of the three piles over, so that it is face up. From the cards in your hand, take the number of cards that corresponds to the number of the card flipped over. For example if a 5 is flipped over, count five cards from your hand and place them aside. Repeat this for one of the other piles.
Now count out how many cards are in your hand, and tell the audience that this is the number of the top card of the final pile. Have the volunteer flip that card over. The number always matches.
(Editor's note: to make this trick seem less "mathematical," don't just count the final cards and say that is the number. Instead, have your volunteer put the cards from your hand onto the last pile. While they do this, you can quickly count the cards in your hand. Now make a production of how you announce the final number.)