I think that was a good first class. (I wonder whether the students think so too.)

After the usual “this is not the kind of math course you’re used to” and “most of you probably don’t want to be here” we started in on “how many seconds have you been alive?” Using curly arithmetic (one significant digit and count zeroes) there are 400 seconds per hour, 10000 seconds per day, 40,000,000 seconds per year, so 1000 million or one billion seconds for a 25 year old.

I’m having a little trouble remembering exactly what happened in class – I *think* that I lost a zero in the my calculation and proposed just 100 million as the answer. Karen Ricciardi (auditing) caught that – but decided not to interrupt. No one in class seems to have noticed.

Half the students had guessed 10 million and half 100 million, so I said half were right, but in fact all were wrong.

What’s my conclusion here? Somehow that part of the class really worked, even though the answer was wrong an no one noticed! I wish Karen had said something, so the students could see that teachers make mistakes too …

Then we moved on to asking whether it was reasonable for Baba Brinkman to claim he’d personally planted a million trees. Half thought yes, half no – most with the beginnings of a quantitative argument, not just an opinion. It was really clear that the answer depended on how long he’d been planting, and on how long it took to plant one tree. The latter number is more important than the former. If 10 minutes per tree, then no way. That 10 seconds per tree is Brinkman’s value makes the claim quite reasonable. I told the Brinkman story as in the text. I wonder how many students will read it, read his blog post at http://www.bababrinkman.com/insult-to-injury/. The lesson is “it depends” – the answer changes depending on the assumptions you make.

This all took a lot less time than I’d planned – I’m not sure why. So we started on the first hw problem – would the plastic utensils abandoned by American in a year go around the world 300 times. We identified the input: how many Americans? How long is a utensil? How big is the Earth?

Maura will teach Thursday’s class (Rosh Hashonah).

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