Percentages.

Tried a new strategy. Prepared three exercises for them to do in groups of three. The handout is here: www.cs.umb.edu/~eb/114/percentages.pdf.

I thought the class was a success – I think the students thought so too. The first exercise did lead to working definitions of absolute and relative change, and the 1+ trick.

I discovered yet again that going around the room explaining the same points in similar words to six separate groups of three people led to some actual visible comprehension, while saying the same words to the class as a whole elicits blank stares. There really does seem to be remarkably little economy of scale in a lecture …

Started on the second problem, and discovered again that almost all the initial difficulty is in the words. What’s a tax refund? A tax bill? Which of the numbers in the quotation are $, which numbers, which percents?

Promised to start next time with finding the number of refunds in 2009 when that number dropped 3.5% to 93 million in 2010. Of course they all want to do this by subtracting 3.5% of 93 million from 93 million.

I think this example introduces two difficult ideas at once: a percentage decrease and a reverse calculation. I will separate them for Thursday.

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