Rectangles for Mathemagicians

May 3, 2012 at 8:22 am 3 comments

Depending who you ask, mathemagician has at least two different definitions:

  1. A person who enjoys both math and magic. (Wikipedia)
  2. A person who is so good at math that the answers to math problems seem to come to them magically. (Urban Dictionary)

When professor Art Benjamin told Stephen Colbert that he was a mathemagician, Colbert asked, “What does that mean? Were those two words by itself not nerdy enough?”

Below is a math puzzle involving magic. To be precise, magic rectangles. But first, a little warm-up…

What do you call a quadrilateral with four right angles that’s been in a car accident?

A wrecked angle.

For the last several years, I’ve had the pleasure of creating puzzles for the Daily Puzzle Challenge at the NCTM Annual Meeting. A new set of four or five puzzles appears in each day’s challenge. The following puzzle, which appeared on Friday’s Daily Puzzle Challenge, involves rectangles and is my favorite puzzle from this year’s meeting.

A magic rectangle is an m × n array of the positive integers from 1 to m × n such that the numbers in each row have a constant sum and the numbers in each column have a constant sum (although the row sum need not equal the column sum). Shown below is a 3 × 5 magic rectangle with the integers 1-15.

Magic Rectangle 15Below are three arrays that can be filled with the integers 1-24, but only two of them can be filled in such a way as to form a magic rectangle. Construct two magic rectangles below; for the array that cannot be used to construct a magic rectangle, can you explain why not? More generally, can you determine what types of rectangles can be used to construct magic rectangles and which cannot?

Rectangles A B C

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3 Comments Add your own

  • 1. venneblock  |  May 3, 2012 at 10:07 am

    I read this post on my Droid X this morning. The images aren’t appearing on my phone, even though they show up just fine on the web. I can’t identify what’s causing the problem. My apologies if you’re reading this on mobile and having trouble, too. I’ll continue to investigate…

    Reply
  • 2. Joshua Zucker  |  May 3, 2012 at 3:11 pm

    I thought “What do you call a quadrilateral with four right angles that’s been in a car accident?” was supposed to be “What do you find in the geometry junkyard?”

    Reply
    • 3. venneblock  |  May 3, 2012 at 4:21 pm

      I’ve heard it numerous ways. What do you call an angle that’s been crushed? What do you call an angle that got hit by a truck? What do you call a quadrilateral that got hit by a bus? What do you call a broken quadrangle? Choose whichever one you like. As I’ve always said, modify the joke to fit your needs and audience. Truth is, it’s a pretty terrible joke no matter how you set it up.

      Reply

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About MJ4MF

The Math Jokes 4 Mathy Folks blog is an online extension to the book Math Jokes 4 Mathy Folks. The blog contains jokes submitted by readers, new jokes discovered by the author, details about speaking appearances and workshops, and other random bits of information that might be interesting to the strange folks who like math jokes.

MJ4MF (offline version)

Math Jokes 4 Mathy Folks is available from Amazon, Borders, Barnes & Noble, NCTM, Robert D. Reed Publishers, and other purveyors of exceptional literature.

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