Get ready to impress even your smartest friends.
Magic tricks often require deception or psychological manipulation, but these 3 tricks are all possible because of math. They are also easy to perform but complicated enough to mystify anyone you try them on. Be sure to take the jokers out of your card deck before getting started.
For this trick, a friend will choose a card, and you will find it in the deck.
First, deal 27 cards facedown on a table and put the rest aside. Have your friend pick a random card without allowing you to see which card it is. Once they’ve looked at it, have them put it back in a random position in the pile so that you can’t memorize where it is.
Deal the 27 cards face-up into three piles of nine cards. Put one card in each pile at a time, and alternate between the piles as you deal.
Have your friend point to whichever pile their card is in. Stack the cards back together, but be sure to put that stack of 9 cards in between the other two.
Repeat what you just did, starting off by dealing three piles of nine cards. This time put the pile with your friend’s card on the bottom of the deck. Then, repeat once more and put the pile on top.
At this point, you are going to deal out the first 8 cards from the top of the deck, and the final card dealt should be your friend’s card.
If you would like to take this trick one step further, you can use ternary counting to manipulate the final position of the chosen card. If you do this, then your friend can tell you how many cards to put down before you reveal theirs. To see how to do this, as well as understand the math behind the trick, watch this video by Mathematical Magic.
2. Find the difference
For this trick, you are going to pick a card and have a friend guess its location in the deck. If you want to make the trick more theatrical, you can pretend that you’re using telepathy to send them the numbers you want them to pick with your mind.
Look through a shuffled deck of cards. Pretend to choose a random card. What you are really going to do is memorize which card is on the top.
Ask your friend to pick a number. Deal out that number of cards from the top of the deck. When you are dealing out these cards, you’re reversing their order, so that the card you chose is now on the bottom of the pile.
Flip over the final card and act disappointed when it’s not your card. Flip that card back over onto the top of the small pile of cards. Take this pile and put it on top of the rest of the deck.
Ask your friend to pick another, larger number. Repeat what you did above and pretend to be disappointed when they don’t get it on their second try. Return this pile to the deck in the same way.
Now you can find the difference between the two numbers. Deal out that many cards and your card will be the last one dealt.
To make sure your friends believe you, you can write down which card you’ve chosen at the beginning of the trick or reveal which card it is just before you deal it.
You can see the trick being performed in this video by Numberphile.
3. Prime factors
For this trick, you need a deck consisting of only single digit cards as well as a calculator. Your friend is going to enter a 6-digit number and you are going to guess factors of that number without seeing it.
Close your eyes and have your friend pick up three cards and enter the number on each card into the calculator in the order they were picked up. Then they will enter the 3 digits into the calculator again, making a 6-digit number.
Keeping your eyes shut, pretend to guess prime factors of the number entered in the calculator. The numbers you will guess are 7, 11, and 13. Have your friend divide by the factor you’ve guessed each time. The number that will end up on the calculator will be the 3 digits they used to make the 6-digit number.
To understand the math behind this trick, check out this video, also by Mathematical Magic.
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