WODB, Philly Style

Given the subject line, you might think I’d ask which of the following doesn’t belong:

So many jokes to be made, so little time.

But actually, I was referring to something completely different.

On Thursday morning, I gave a talk to 850 enthusiastic teachers at the School District of Philadelphia‘s Summer Math Institute. That may be the largest group to which I’ve ever spoken; it certainly exceeds the 600+ to whom I delivered my Punz and Puzzles talk at the North Carolina Council of Teachers of Mathematics conference, and it likely exceeds the number of people who heard me sing a karaoke version of Liz Phair’s Girls! Girls! Girls! after a half bottle of tequila — although that’s a story for another time. (Yes, I know all the words. But I’ve said too much.)

I was going to begin my talk in Philadelphia with the following warm-up question,

Quadrilateral MATH is similar to ATHM. What can you say about MATH?

because I wanted to ask the follow-up question,

What can you say about math?

taking advantage of the double entendre caused by MATH (a geometric figure) and math (an academic subject). Clever, no?

But I was worried that a high-school level geometry question might overshoot my audience of K‑8 and Algebra I teachers. So I was looking for an alternative.

That’s when Jen Silverman — to whom I owe a huge thanks and several pints — suggested that I do a Which One Doesn’t Belong using the letters M, A, T, and H. Based on her suggestion, I created this:

It led to a great discussion, both mathematical and otherwise. So, here’s my challenge to you:

Which letter doesn’t belong?
Post your choice and explanation in the comments.

If you’re not familiar with Which One Doesn’t Belong, then check out http://wodb.ca or follow @WODBMath.

I had always thought that the #WODB movement began with Christopher Danielson’s “better shapes” book, Which One Doesn’t Belong (forthcoming).

But then I found this activity sheet in Navigating through Problem-Solving and Reasoning in Prekindergarten and Kindergarten, which was published by NCTM in 2003:

So WODB is at least 13 years old, probably more. Anyone know exactly when or where it started? I’d guess Lola May, though that’s purely speculative.

Huge props to Karl Fisch, who posted the funniest WODB to date:

Well played, Karl, well played.