It was hard for today’s class not to be a letdown after last Thursday’s. And it was, some.

I realized over the weekend (writing answers to the homework problems I’d assigned) that I asked too many that required finding one missing value in an averaging problem when the weights are known. The mathematics is interesting (easy algebra, or guess and check) but the problems themselves are not in fact realistic, so we shouldn’t be spending time on them.

I did work the problem 6.10 based on a quote from an old edition of the Hightower Lowdown, by popular request. I stumbled myself through the arithmetic (saved only by a student who pointed out my misplaced decimal point). I need to rewrite the question in the book, or delete it, or (at least) warn instructors not to assign it or too many like it. What I should have asked was “what political point is the author trying to make by including these particular statistics?”

We talked then about two ideas described in the book that I wanted to make sure the students had been exposed to. (In fact, we didn’t talk – I talked – probably not wise.) One was the CPI market basket – the weights for the various categories the Bureau of Labor Statistics uses to calculate the average inflation rate. The other was the class size paradox, discussed in the book. The main point I wanted to make there was the value of studying a phenomenon by imagining an extreme case – in this case one professor with two classes, one empty and one with 100 students. The professor’s average class size is 50, each student’s is 100. Along the way we thought about the words “paradox” and “oxymoron“.

With half an hour left, we started the Excel tutorial in Chapter 7. I think the class was relieved.

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