Math Clocks

September 29, 2010 at 12:18 pm 4 comments

Jiminy. The folks at Clock Zone make a math class wall clock — and I would like to be the first to publicly chastise, amazon, and anyone else who is selling it. It contains at least two mathematical errors:

SPOILER ALERT: In my rant below, I identify the errors in the clock. If you’d like to identify them for yourself, don’t read any further.

I say “at least” two errors because there may be more. The obvious errors are for 9 (the expression assumes that the exact value of π is equal to the common approximation 3.14) and for 7 (because the equation is quadratic, x = 7 is only one of the answers; the other possible answer is x = ‑6).

More generally, I have an issue with any of the algebraic equations that are meant to represent integers. For instance, the equation 50/2 = 100/x has solution x = 4, but I believe that it is incorrect to say that the equation itself is equal to 4. So perhaps the clock has four errors, if you consider the algebraic equations for 4 and 10 to be erroneous, as I do.

This clock is meant to be a math joke. Edward de Bono in The Mechanism of the Mind (1969) suggested that when a familiar connection (such as seeing the numerals 1‑12 on a clock) is disrupted, laughter occurs as a new connection (seeing mathematical expressions instead of numerals) is made. Sadly, math jokes are supposed to make you laugh… yet this clock makes me want to cry.

To ease the pain, I did a little research and uncovered several clocks of famous mathematicians. I present them here for your enjoyment.

Leonardo da Pisa:

Kenneth Appel:

Rene Descartes:

Karl Friedrich Gauss:



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4 Comments Add your own

  • 1. Justin  |  September 29, 2010 at 5:18 pm

    I consider the square roots an error for the same reason as the quadratics: there are two solutions. The quadratics have the additional problem that they are equations, not values.

  • 2. Larry Davidson  |  September 30, 2010 at 6:04 am

    No, Justin, the square roots are not an error! While it is true, of course, that 4 has two square roots, the symbol used on the clock means “the principal square root.” Since the principal square root of a positive number is a positive number, the clock is actually correct in this regard.

  • 3. Molly Hopkins  |  October 24, 2013 at 12:48 am


    • 4. Molly Hopkins  |  October 24, 2013 at 12:50 am

      Oh wait are those commas? My screen isn’t very high def😦


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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.

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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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