## MJ4MF and Math Clocks

*August 8, 2015 at 6:05 am* *
4 comments *

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:

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1.goldenoj | August 8, 2015 at 12:45 pmWould 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 pmThat’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

xto find the time. Why not just an expression instead of an equation?3.Arthur Benjamin | August 8, 2015 at 3:45 pmThe root 4 and root 64 are also very problematic, since they have positive and negative values.

4.venneblock | August 11, 2015 at 12:35 pmI 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!)