Plan. Finish class work on percentage calculations. There should be questions, but if there are none then this will be brief. I think I will shortchange the inflation chapter – perhaps show them the BLS calculator, use it to reinforce the fact that inflation is a rate, perhaps do two in a row to use the 1+ trick again. I’ve prepared two exercises in a handout to cover that.

I’d like to get to (weighted) averages pretty soon. I can revisit inflation by assigning the exercise on how the CPI is calculated as an average.

What happened:

This first one was pretty straightforward:

• Use the in ation rate calculator to nd the in ation rate (as a percent) from 1990 to 2000, from 2000 to 2010 and from 1990 to 2010.
• Explain why the inflation rate from 1990 to 2010 is not just the sum of the ratefrom 1990 to 2000 and the rate from 2000 to 2010.
• Use the 1+ trick to compute the 1990 to 2010 rate correctly from the rates for the two previous decades

Going around the room I found that most students knew they could start by entering any amount they wished in the BLS calculator, but few realized that starting with $100 would make the job easiest. I think the exercise did reinforce the fact that percentages are rates. I’m not sure the 1+ trick worked all that well for most of them.

The second problem turned into the usual nightmare:

Over the last decade, in ation-adjusted wages in Columbia Countydropped 13.8 percent, while salaries in nearby Oregon counties grew orremained mostly static. A report released June 1 by the Oregon Employment Department and the Bureau of Economic Analysis shows between 2000 and 2011, the averagewages for . . . jobs in Columbia County rose by 13 percent. But countywages actually decreased 13.8 percent during that time when in ation istaken into account.In neighboring Clatsop County, . . . (t)he in ation adjusted wages . . .rose 0.4 percent from 2000 to 2011.

Just reading the words was a serious problem. The tutor and I worked with one table (of two or three) at a time suggesting that they start with $100 in  2000, which would be $113 in 2011 after the raise, and then use the BLS calculator to see what $133 in 2011 would have bought in 2000. Two students who “got it” after an explanation went around the room helping others.

In the end the qualitative “adjusted for inflation, there was a pay cut, not a raise” made sense to them. I didn’t even try to get the numbers to match.

On to weighted averages. I asked what a students average would be in a hypothetical course where her grades were 70% on the hour exam and 90% on the final. One student said “it depends on what each is worth” which was, of course, the whole point. I worked out the answer with weights of 25% and 75% – the average grade is then 85%, which made sense to most. Next time I’ll do GPA, and a homework problem on the CPI.