Exploratorium
Mind Reader    
Instructions
These instructions tell you how to do a cool card trick that's guaranteed to make you look like a mind reader. Try it with a friend, then spring it on some unsuspecting victims—like your parents!


What Do I Need?
A deck of cards
A friend
A pencil and paper
 
What Do I Do?

Step 1
Shuffle the deck. That way your victim—oops, your friend—knows you haven't done anything weird to the deck of cards.

 
Step 2
Ask your friend to choose any card from 1 (ace) to 9, but not a 10, jack, queen, or king. Tell them not to show it to you, but to memorize the number on it.

Step 3
Tell your friend to put his or her card on the table, face down.

Step 4
Now you take a card from the shuffled deck. Choose a card with a number from 1 (ace) to 9. Don't choose a 10, a jack, a queen, or a king. Don't show the card to your friend.

Step 5
Memorize the number on the card, then lay the card face down on the table on the right side of your friend’s card. Be sure that your card is to the right of your friend’s card.

Step 6
Now comes the "magic" part. Give your friend the paper and pencil so that he or she can do some math. Now tell your friend to do the following things—without showing you the answers:

 
What you tell your friend to do:   Example:
    Suppose they have the 3 of hearts:
Double the value of the card.   3 * 2 = 6
Add 2 to that number.   6 + 2 = 8
Multiply the result by 5.   8 * 5 = 40
Step 7
So far, your friend has been doing all the math. In this step, you have to do a little math in your head. Take the number of the card you chose. (You remember what it is, don't you?) Then do the following:

 
What you do:   Example:
    Suppose your number is 8
Subtract the number of your card from 10.   10 - 8 = 2


Step 8
Now it’s your friend’s turn again.

 
What you tell your friend to do:   Example
Tell your friend your answer from Step 7.
Have your friend subtract that from the number he or she got after doing all the math in Step 6.
  40 - 2 = 38
Ask your friend to tell you what number he or she got after doing all that math.   Our friend said 38


Step 9
Here’s the magic part. Flip over your friend's card on the table, and then your own. There will be the two digits of the number your friend said. Enjoy the shocked look on your friend's face!


 
Step 10
But wait! Suppose your friend came up with a different number. Mutter something like, "I know the magic worked—so let’s check your math." Check the math—and you will get the number that’s on the cards.

 

 

Why Does This Trick Work?

Find out at Analyzing Mind Reader.

Next

 


For tips on how to use this trick with a class or group, go to the Teacher/Leader version.

 

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