Carry on conjuring

You gather up the pile of cards from your last trick after triumphantly revealing the card the volunteer was thinking of (perhaps the 21-card trick). You now show that you can not only read minds, but also see into the future.

First, you write a prediction on a piece of paper and seal it in an envelope so no one sees your prediction. You give it to a member of the audience to hold so that the sealed envelope remains in clear sight and cannot be tampered with.

Next you ask the spectator to cut about half the pack off the top. They decide how much, free choice. They are going to select a card from the top half of the pack that they just cut off but even they aren't going to know which one it will be.

They deal the first card face down on to the remnants of the pack, and the next card face up on the table, next card face down on the remnants of the pack, next face up on the table, and so on.

Once they have finished with the cards in their hands they start again, picking up the face up pack turning over and dealing the first face down on the pack remnants and the next face up, until all cards are dealt.

Again they pick up the face-up cards and deal in the same way. They continue doing this until they have exhausted the cards in their hand and there is only one left face up on the table.

You recap for the audience: a free cut of the original pack, a fair deal to eliminate all but one from their original free choice, a sealed prediction written at the start.

Now you reveal your prediction from the envelope...you predicted the card that is now face up on the table!

Magical mind reading...or is it?

To find out how to make the trick work and its link to Computer Science, follow this link.