Fun Math Tricks

Telephone Number Mix-Up

• Ask a volunteer to think of a 7-digit number: it could be a phone number or any other 7-digit number they want to come up with. They can tell you the number.

• Have them write their 7-digit number down on a sheet of paper.  

• After they write their number down on the paper, you will then announce to your spectators, 

"I'm going to now make a prediction and write it down on this piece of paper and at the end of the trick, I'll uncover my prediction."

• You will then, write down your prediction on a different piece of paper without letting them see it and turn it face down. Your prediction will be disclosed at the end of the trick for the grand finale!  


• Next, have them mix up the digits in their 7-digit number in any way they'd like and write that number down on the paper. 

Example:

Original number: 9 2 8 4 1 2 0

Mixed up number: 2 0 2 1 9 4 8

• Have them subtract the smaller of the two numbers from the larger one:

9 2 8 4 1 2 0 - 2 0 2 1 9 4 8 =

7 2 6 2 1 7 2

• Now have them add up the digits in the difference they got from subtracting the two numbers:

7 + 2 + 6 + 2 + 1 + 7 + 2 = 27

Now for the cool part!

• Have the person use the sum they just got in the previous step (for this example, 27) and starting from the number 1, count clockwise around the circle, landing on the next picture as they count around the circle. 

Print Circle here

***  Important  ***

They should begin their count starting on the picture below: 

• After counting clockwise around the circle, they'll always end up on the picture that you predicted - the black star shown below!