Twenty-One Card Trick

The game uses a selection of 21 cards out of a standard deck.

Minor aspects of the presentation are adjustable, for example the cards can be dealt either face-up or face-down.

If they are dealt face-down then the spectator must look through each of the piles until finding which one contains the selected card, whereas if they are dealt face-up then an attentive spectator can immediately answer the question of which pile contains the selected card.

The magician begins by handing the spectator the 21-card packet and asking them to look through it and select any one card to remember.

If the magician gathers up the piles again, as before with the pile containing the selection in the middle, the selection will be the eleventh card in the 21 card packet.

Mathematical explanation of the Twenty-one card trick with 27 cards:
In each step, the cards are dealt into three piles. The piles are accumulated with the pile containing the target card (shaded yellow and labelled with the step number) put in the middle.
After three steps, the middle card (*) is the one in all chosen piles.
Animation demonstrating how the 21-card trick method excludes incorrect cards each time a pile is selected, leaving the selected card in position 11.
Animation demonstrating how the method excludes incorrect cards each time a pile is selected, leaving the selected card in position 11.