Mind-Reader Card
Place 12 cards on the table, using any cards from the deck, 6 of each color, in the same pattern as in the diagram above. Ask a volunteer to secretly choose any black card.
Ask her to move -- without touching the cards or letting you know which card she's on -- up or down to the nearest red card. (She may have to skip over a black card to get to a red one.)
Next, tell her to move left or right to the nearest black card.
Next, tell her to move diagonally to the nearest red card.
Finally, ask her to move up or down to the nearest black card. Tell your volunteer that you know exactly which card she is now on, and name the middle card in the bottom row!
This trick works because the specific arrangement of colors and moves forces the volunteer to end up on the middle card in the bottom row. Many of the moves will have only one possible direction; for example, there may not be a red card below, so she has to move up. Thus, no matter where she starts, her next-to-last move will always land her on a red card in the middle column, and her last will move down to the “mind-reader” card, because there is no black card to move “up” to in the middle column!
The Rock Concert Trick
Read all of the way through this trick first, so that you are sure you know what’s coming. First, go through the deck and pull out all of the aces, kings, queens, and jacks. It’s okay for the audience to see this. Lay the rest of the deck aside; you won’t be using it. This trick has a basic "patter" for you to say as you perform it. You will "say" the parts in quotation marks, and [do] the parts in square brackets. You can use the name of your favorite singer or band; feel free to add details to the story.
"The Ace family is going to a rock concert." [Lay the aces face-up on the table in a row as in the illustration above.]
"The King family is also going to the concert, and they chat with their friends in line." [Lay the four kings face-up on top of the four aces, so that all cards are visible.]
"Then the Queen family joins up with their friends, the Aces and the Kings." [Lay the four queens face-up on top of the previous stacks.]
"The Jack family is also going to the concert, and they meet their friends in line." [Lay the four jacks face-up, in the same way.]
"Now it’s almost time for the concert to start, so the four families head off to their seats." [Turn over each stack, one at a time, so that they are face-down.]
[Pick up the first stack and place it on top of the next stack, then pick up this new, bigger stack and place it on top of the next one, and again with the last stack. It doesn’t matter whether you go left to right or right to left. You now have one big stack of cards.]
Ask for a volunteer from your audience, and say to her, "Okay, cut the cards by taking a group of cards off the top of the stack and placing them on the table, then put the remaining cards on top of the stack. Cut the cards as many times as you want." [Let her cut the cards a few times, then deal the first four cards face-down in a row, then the next four cards on top of the first four, and so on -- just as you did when you first dealt them out, except that this time they are all face-down -- until all sixteen cards are dealt out.]
"Now each family is sitting together, enjoying the concert!" [Turn over each stack to reveal that the kings are all together in one stack, the queens are together, and so on.]
How this trick works: After you have dealt out the four “families”, each stack is in a specific order: ace, king, queen, jack. When you turn them over and make one big stack, the cards are still in this order, but it is repeated four times: ace, king, queen, jack, ace, king, queen, jack, and so on. When you cut the cards -- it must be done in the way described above, not in a random shuffle-- you are actually keeping the cards in the same basic order, just starting at a different point in the sequence. For example, at the beginning, the cards are in the order A K Q J A K Q J etc. After two or three cuts, it might go Q J A K Q J A K, but it is still the same sequence, just missing the first two at the beginning (because these are now at the end). When you deal out the cards in the last step of the trick, you are actually sorting them into their "families", although you won’t know where in the sequence you are starting until the reveal at the end.
Mysterious Math Card Trick
Start with a 52-card deck.
1. Have your volunteer shuffle the cards any way she likes, as many times as she likes. When she is finished, show her the bottom card so that you cannot see it, and tell her to memorize that card.
2. Turn over the top three cards, and place them in a line.
3. Deal cards face-down below each of these three cards in the following way: Start with the value of the first card (ace = 1, jack = 11, queen = 12, king = 13), and then keep dealing cards in a stack below that card until you get to 15. For example, if the first face-up card is a 9, you will deal six more cards face-down to get to 15. Repeat with the other two stacks.
4. Leaving the three face-up cards on the table, put all of the face-down cards on the bottom of the deck.
5. Ask your volunteer to add up the total value of the three face-up cards; for instance, 9 + queen (12) + 10 = 31). Deal out that many cards face-down, and put them on the bottom of the deck.
6. Tell your volunteer that you will now reveal her card. Lay out four cards face-up, one by one — the fourth card will be the one that your volunteer memorized!
How this trick works: The object is to eventually remove all of the cards from the top of the deck in order to get to the target card at the bottom (the card you showed to your volunteer). Remember that the deck has 52 cards. The three face-up cards removed in Step 2 leave 49 in your hand (52 - 3). Now, in steps 3 through 5 you will remove a total of 45 cards, 15 for each face-up card (or 15 x 3).
Let’s look at only one stack for a moment: In step 3, you deal out some number of cards to get up to 15, then in step 4 you put those cards at the bottom of the deck, and then in step 5 you deal out the remaining cards to total 15. Looking again at all three stacks together, you will always take off 15 + 15 + 15 -- it might be 8 + 7 in one stack, it might be 11 + 4 in another, but each will always total 15. (This is a variation on the associative property of addition, which states that changing the grouping of addends does not change the sum.)
When you put these 45 cards (15 + 15+ 15) on the bottom of the deck, you force the target card closer to the top of the now 49-card deck (52 - 3 face-ups). Since 49 - 45 = 4, taking away four cards will bring your target card to the top!
Adapted from a trick posted by Raymond Blum at education.com.
