Last Thursday was a snow day. Today we continue with percentages, working on the homework due Thursday. I hope to get to the 1++ trick. Maybe I’ll start with that. This Thursday (day after tomorrow) we’ll meet in the mac lab, so we have access to the computers for the inflation calculator, and so they can find the room next week for the exam.
I think the class went well. I did the backward computation on the board for the class. As soon as I started with the question about a 3.6% increase to $1355 and wrote
$1355/(unknown original value) = 1.036
the silence in the room told me I needed to backtrack. So I did the Red Sox ticket example over again starting with
$52.16/42.26 = 1.23
which implies a 23% increase. (Before the people in the class with calculators on their phones reported that answer I explained how we could know in advance that the increase would come out about 20%.
Then I asked how we could compute the old value if we knew the $52.16 and the 23%. It wasn’t hard then to come up with
$53.16/1.23 = …
We did several more problems that called for the 1+ trick – in particular, a 20% pay raise followed by a 20% pay cut doesn’t come out even. Nor does it if the cut precedes the raise.
Did the homework exercise about for-profit colleges spending 23% ($3.7b) on advertising, collection 86% of revenues from the federal student loans. The numbers are easy to work with once you understand what they mean. You can only know that by understanding the story the article tells, and reading the words carefully.
We’ll meet in the Mac Lab Thursday, so they can find the lab before Tuesday’s exam. I told them the exam would be open-everything, probably too long, that they’d have a chance to redo it for homework and that it was seriously curved, so that if the highest grade was, say 75, then that would be an A. And I reminded them that they could take the course pass fail.
In principle, I like to think that everyone in the class is there to learn as much as possible, with my help, and that neither of us cares about attaching a grade to that work.
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