Monday, June 21, 2010

Challenge: Do a Mathemagical Performance








1Contest ends at the end of summer, September 20.


  1. I have another trick. Ask a volunteer to choose some integer and write it down on a piece of paper. Ask volunteer 2 to write down some other integer which has all the digits of the first number rearranged in some order. Ask volunteer 3 to verify that volunteer 2 did his/her job correctly and then give him/her a calculator to compute the difference between the two numbers and write it down. (this difference is a multiple of 9, which can be shown through modular arithmetic)

    Now you claim that you can tell them the last digit of the difference if they tell you the rest of the digits of the difference. For 8 of 9 cases, this isn't a problem. When the rest of the digits also add up to a multiple of 9, the last digit can be 0 or 9. Under such situations, it is advisable to steal a trick (sorry, illusion) from Gob (of Arrested Development). Hide a playing card with the number 9 in a shirt pocket and guess 0. If it fails, pull out the card as some sort of dramatic apology.

  2. Very tempting this is...

    Some resources:
    Arthur Benjamin's TED talk
    Bradley Field's Mathemagic site
    Some easier math-magic tips.

  3. Hi Sue! I hope you don't mind that I put your blog address on my site. I'm looking forward to your book.

    I also wanted to let you know that in about 15 minutes there will be a Trinomial Factoring Proof animated video on my site. I was inspired by a Professor jack Rotman's simple explanation of why we multiply AC to fond the factors that should add to B in a trinomial. Good stuff. I hope you like my video! It'll be on my blog ( right after it finished uploading onto YouTube (

    Thank you for the suggestion to make a video proof. I'm excited for people to see it (and comment or complain!)

  4. Thanks, Hao, that's a good one. Now we have three tricks in our performance bag.

    And thanks for the links, John. Maybe we could squeeze in a Grand Haven beach performance together!

    ZSR, thanks for mentioning my blog on your site, I'm honored. And I'd love to chat by email about those videos. I'm at suevanhattum on hotmail.

  5. I can't think of a better way to "make a fool out of yourself" than doing math and hopefully making a bit of cash as well. Good Luck.

  6. - Give me a number between 1 and 100
    - 57
    - 58, mine is larger, I win!
    - No fair - you go first this time.
    - Sure. 100.
    - ...
    - I've been playing this game for a long time!

  7. Maria, that's great! (If I can pull off the right comic touch...)

    Another trick here.

  8. Put your pants on inside out, tie a rope around your ankles, and then get your pants on correctly without removing the rope. :)

  9. Sounds a bit risque (sp?)... Seems like a good math clowning act for a guy. Bright shorts under balloony pants...


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