Mental Math Magic

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Mental Math Magic

For those of us who love mathematical magic, here is a beautiful effect that you can do anywhere, anytime, with any deck. All you need is to be sober and able to do a little simple subtraction.

With your back turned... ask Scott to write down a four digit number, any number. Now, ask Scott to add together the four digits and subtract them from the original four digit number. Example: Scott writes down 3941. He adds 3+9+4+1 = 17. Scott subtracts 17 from 3941 and arrives at 3924. Have Scott look through the deck and find four cards who's numerical value equals his total. Also, ask him to make sure the suit of each card is different from the other three. So, Scott finds a Three of Hearts , a Nine of Spades, a Two of Clubs, and a Four of Diamonds.

Ask Scott to secretly remove one of the four cards and put it in his pocket. He can lay the other three face up on the table as you have no way of knowing the fourth card... or do you?

Looking at the three cards, you will immediately know the suit. Assuming Scott put the Nine of Spades in his pocket, it's obvious the Spade card is missing from the table.

Remember three key numbers... 18, 27, and 36.

Mentally add together the total of the cards on the table. In this case it's a 3, a 2, and a 4. So, 3+2+4 = 9. Subtract your answer from whichever of the three key numbers is immediately higher than your total. In our example, 9 from 18 equals 9. Sound familiar?

Nine is the number in Scott's pocket. A Nine of Spades - to be exact.

If the three cards had totaled say.. 22, then you would have subtracted 22 from 27, and the card in the pocket would have been a Five.

Don't ask me why it works... it just does. OK...

   

Comments

9/10/2010 2:12:06 PM
Macoto said:

What if the number is a 0


9/12/2010 12:33:36 AM
Rick said:

If the number is a zero, advise the spectator to use a ten to represent the zero, as the ten will not be used normally anyway.


10/22/2012 2:51:50 PM
Jerry said:

Let's say the number is 8123 and they get 8109 for example... If they show you 8, 1, and 9 you get 18. Now if you subtract this from 27 you are left with 9, but if you subtract it from 18 you are left with 0 and you know it's a 10. How do you know if the number is a 10 or a nine in this instance?


2/21/2013 8:51:41 AM
sirocco said:

what if he says 1111-4=1107
he picks 7, I have the 1+1+0=12
18-12=6 trick failed.
I think the description is missing something. Maybe should ask for a 4 digit number with different values?


4/29/2013 12:57:21 AM
Rick said:

1+1+0 equals 2 not 12. 2 from the nearest multiple of nine is 9-2= 7.. Hope this helps..


4/29/2013 1:04:46 AM
Rick said:

If they arrive at a number that has a zero, ask them to NOT keep the zero as the hidden number.. " as it has no value "..


3/19/2015 1:37:10 PM
Paul Barnett said:

Another of the magic numbers is 9

You are effectively using the 9 times table to solve this problem. What ever the value of the cards that are displayed (1-99) you subject from the next highest number in the 9 times table.

So if the number is 1-8 subtract from 9

if 11-17 subtract from 18

if 19-26 subtract from 27 and so on

Paul




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