Wild About Math! Making Math fun and accessible

15Jul/103

12 cent Math trick

Here's a very interesting and simple trick to impress your friends. It's simple enough to do that even the little ones, if they can count to 12, can do this trick. There's no sleight of hand or any other difficult manipulation to do. In fact, once you know the very simple steps, the trick is pretty automatic.

The trick is based on some very simple algebra but I've found that even though I understand how the trick works it's still eerie to see it work.

I got this trick from Shecky's great Math-Frolic Blog. The trick was developed by Alfred Posamentier, a prolific writer of Math books. While Posamentier is not as well known as Martin Gardner or Cliff Pickover, his books are equally engaging.

I rewrote Posamentier's trick so that it could be performed as a bar trick so that maybe Scam School will pick up the idea and produce a video of it.

Here's my version of the trick:

The scamster hands the victim 12 pennies and then blindfolds himself. The victim is instructed to place the coins on the table such that exactly five of them are heads up. The scamster tells the victim that he can, without removing the blindfold, separate the 12 pennies into two groups, and turn over some pennies so that each group will have exactly the same number of coins heads up. Fumbling around because he can't see, the scamster moves the 12 pennies close together into a group and then somehow picks some of the pennies and moves them to another group. He then turns some coins over and, voila, both groups have the same number of heads up pennies.

How can the scamster know how to separate the coins into two piles? How does he know which coins to turn over? How can he do this all blind-folded? See if you can figure out the trick on your own then head on over to Shecky's blog for Posamentier's solution.

Filed under: Algebra, Trick Leave a comment
Comments (3) Trackbacks (1)
  1. Nice trick! Thanks for posting.

  2. I recall a similar trick with cards (so that the scamster cannot even feel if the coins are heads or tails up)

    And I do not like Pickover’s books :-)
    (dunno about Posamentier, I’ll try and buy one of his books)

  3. I stand corrected, I have Challenging Problems in Geometry :-)


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