MJ4MF and Math Clocks

How stoked was I to see that @WeAreTeachers is giving away a Swag Bag that includes a copy of Math Jokes 4 Mathy Folks? In a word — inordinately!

My only concern is that the bag of goodies also includes this clock:

This is the second time in less than two weeks that I’ve seen this clock. I was disheartened to see it hanging in a middle school that I visited recently. I believe that no self-respecting math teacher should be willing to display it. Cute? Yes. Mathematically accurate? No. To wit:

• Painful: The equation 50/2 = 100/x yields the solution x = 4. But an hour after 3 o’clock is 4 o’clock, not “x = 4 o’clock.” This equation should be replaced by the expression 2 × 100 ÷ 50. Similarly, the equation -8 = 2 – x should be replaced by -8 – (-2).
• Just Plain Wrong: So, maybe you have no problem with the use of a equation on this clock, and you’re okay that the solution of the equation is meant to represent the missing number. Okay, fine. But there can be no way that you have no problem with the equation at 7 o’clock. It’s quadratic, so there are two solutions. C’mon! Anyone who solves that equation won’t know if it’s 7 o’clock or -6 o’clock!
• Egregious: When the big hand of this clock points north and the little hand points west, the time will be 9.00477796077… o’clock (or thereabouts). Teachers spend a good part of their lives trying to help students unlearn that π = 3.14. It’s not; that’s only an approximation. Yet this clock perpetuates that misconception.

I would like to suggest that the folks at We Are Teachers consider including a different clock in their Swag Bag. I’m a much bigger fan of the Math Expressions Wall Clock:

Or perhaps one of these Math Clocks would be more appropriate:

Entry filed under: Uncategorized.

• 1. goldenoj  |  August 8, 2015 at 12:45 pm

Would you feel better if the quadratic for 7 was x^2-2x=35? (I would.)

The pi is problematic, regardless, though. Maybe a complex factorization of 9?

• 2. venneblock  |  August 11, 2015 at 12:43 pm

That’s fantastic, Math Hombre! But no, I wouldn’t feel a whole lot better. I still don’t like that we have to solve for x to find the time. Why not just an expression instead of an equation?

• 3. Joseph Bell  |  May 31, 2017 at 9:22 am

x^2-2x=35… x could be -5 or 7… *facepalm*

• 4. venneblock  |  June 6, 2017 at 4:38 pm

Wow, I totally missed the double entendre with goldenoj’s suggestion. Fantastic!

• 5. Arthur Benjamin  |  August 8, 2015 at 3:45 pm

The root 4 and root 64 are also very problematic, since they have positive and negative values.

• 6. venneblock  |  August 11, 2015 at 12:35 pm

I left that one alone, Art, because of a lot of recent discussions of the principal square root. I don’t remember that term existing when I was in school… but I’m more of a descriptivist than a prescriptivist, and if that’s the way convention is going, so be it. (Though in private, Art, I’m totally going to agree with you!)

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.