Monday, June 21, 2010

Challenge: Do a Mathemagical Performance

One of the members of the Natural Math group pointed us to a BBC article, "Taking Maths to the Street." The author of the article (who isn't big on math) and a bunch of math teachers and students get trained to do math tricks and then go out on the street, trying to entice people to watch them. She called it 'busking.' I think that includes putting a hat out for donations, but she didn't mention that part. I was disappointed that the author didn't manage to do her trick properly. Is her article perpetuating the myth that math(s) is too hard for 'regular people' to get?

My math poem challenge back in January was a hit, so let's try it again. This time the challenge is to do some street performing using math. I think it's a great way to show the world that math can be fun. Should we have a way to determine a winner? Should it be the one who gets the most money in their hat?1

You might want to do this with a few friends. Having a group of you, like they did in the article, might make it easier to attract attention. And maybe it would be a good idea to wear some cool math shirts. I'd like mine to say mathemagician. I wonder if I could find something like that... Yes...

I'd love some discussion here about other tricks that would work well for this. The article mentions two: The first, determining the day of the month of someone's birthday by which of five cards they say it shows up on, is based on binary. The other trick is a variant of Nim - each player takes from one to three post-its off the assistant on their turns, and the post-it with the $20 bill attached must be the last one taken off.

The article's author used 8 post-its. I think this trick would be more mysterious if you started with more. I'd recommend asking the volunteer whether they want to go first or second while you're putting the post-its on your assistant. If they want to go first, you could put on 16 (or any multiple of 4). If they want you to go first, you could put on 17 to 19 (or anything not a multiple of 4).

I could probably go over to SF and try this by the Powell Street Cable Car stop; there's usually a long line there. If I can find some else willing to be a fool for math2 with me, I promise to do it at least once. (Is anyone reading this from the Bay Area?)

Who else is game? Step right up! Getcher number here!

1Contest ends at the end of summer, September 20.
2I wrote this full of enthusiasm yesterday morning. Now I'm a little nervous. But hey, it's a small commitment, and if it bombs, I don't have to do it again, right?


  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...


Math Blog Directory