25 July 2012 - Card Trick

This is a math-based trick, so you may not be able to play it on anyone who is younger than 8 or so, depending on how good they (and you!) are at math.

Take a deck of cards and take out all the 10s, Jacks, Queens and Kings (there are 4 of each).  You also should make sure you don't have any Jokers in the deck.

Ask for a volunteer and tell them they are going to pick 2 cards and you will tell them what they are.  Tell your volunteer to pick one card and look at it.  In their head (or you could give them paper) tell them to do the following steps:

1.   double your number

2.   add 5 to your new number

3.  multiply your most recent number by 5

Finally, they need to pick another card and add that number to whatever they had last.

Have them tell you their final number.

In your head, subtract 25 from their total.  The 2 digits of whatever you have left are the 2 cards they had.

EXAMPLE: (volunteer picks an 8)

1.  double your number = 16

2.  add 5 to that number = 21

3.  multiply by 5 = 105

Pick a second card (we'll say it's a 3)  Add that to your last total 105 +3 = 108

They will tell you their number is 108

 In your head, you figure that 108-25 = 83.  So their 2 cards were an 8 and a 3!!

EXAMPLE 2: (volunteer picks a 2)

1.  double your number = 4

2.  add 5 = 9

3.  multiply by 5 = 45

4.  second card (we'll say it's a 9).  Add to last total 45 + 9 = 54

They will tell you their number is 54

In your head, subtract 54-25 = 29.  So their 2 cards were 2 and 9!!

 Try it by yourself a few times first, so you get the hang of the steps and the math.  Then try it on someone else and see it in action.  Tell us in the comments section if you tried it and if it works.

Let's pretend I was your volunteer!  My total is 69.  What were my 2 cards?

I volunteered again!  My total is 41  What were my two cards?

Post your answers as a comment and I will let you know if you were right.