## Archive for August, 2015

### 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: