Suddenly the semester seems nearly over. Three more classes ’til Thanksgiving (counting today), then a few weeks after. It’s time to begin thinking about what to leave out. There’s no point racing through a syllabus just to say you’ve covered the material. So income tax (piecewise linearity) is out. So is most of energy and power. Not sure how much to do on exponential growth (in the abstract) and exponential models. Then I should have time for credit card debt and the probability chapters.

Gave back the exams. There were a bunch of C’s and some B’s. Only one real A. Most of the D/F students have withdrawn, or are taking the course pass/fail. I didn’t want to promise too much at this time in the term, but I’m pretty sure there will be more A’s at the end. (If the good students are reading this blog that will encourage them.)

For real work I went straight to regression. I worked the Pisa example from the text as a tutorial. Then I looked at the correlation between life expectancy and number of TV sets per person to make a point about correlation and causation. Didn’t work too well – the data aren’t very highly correlated and the graph is weird. Consider removing the problem from the book. Moved on to the crime-falls-fears-rise example in the text. That one worked really well.

So … having worked through all of Chapter 9 (!) I had a few minutes. To pave the way toward thinking about credit card debt I worked out the first few years comparing $100/year and 8%/year interest on a $1000 investment. The second provided a review of linear equations, the first a review of the “1+” trick for percentage growth and an exponential equation. I promised to start the next class by redoing this material.

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