16 cards with different numbers and shapes on them are scattered on the table. In addition a different card with a question mark is laid on the side without calling attention to it. The magician point to the fact that some cards have similar drawings, colors or letters on them. He shows that groups of cards which all have the same letter, color or drawing on top may add up to a different total.
Now, the spectator is being asked to pick up a group, for example, all cards with a blue background, all cards with the letter "A" on them, etc. etc. Ask him to sum up all the numbers, and read it out loud. Turn over the card with the question mark printed on top and show that the number he reached is identical to the number on the other side of the question mark card!!!
