Saturday, January 28, 2012
I've half a mind
When it's early in the semester, I tend to cut my students a little more slack. Of course, I expect them to pay attention when I explain why I take off points for some calculations that manage to produce correct answers. For example, how many minutes does it take you to travel 12 miles at 18 miles per hour? Here's what one student told me:
Yeah. Well, I'm really not happy with that. Sorry, but 12/18 is simply not equal to 40. Equality is supposed to be a transitive property, folks! Of course, this could be redeemed with the appropriate use of unit conversion:
This I like. Careful use of units is a powerful way to keep one's calculations in order and to make sense of the results. Full marks! But then you get the woefully calculator-dependent student who presents this travesty:
Heck, you can keep your puny old leap-seconds! My students can conjure up a dozen seconds out of the thin air of feckless rounding. This is a particular gripe of mine. You actually need to grab for a calculator to compute two-thirds of sixty? Good grief!
Thoughtless calculations like these were sprinkled throughout the early semester quizzes and exams. But the pièce de résistance came in a different problem. One that had nothing to do with rounding. I gave my students (gave them, mind you) some volume formulas. All of the most popular shapes were there: cone, cylinder, sphere, box (ahem! Sorry. I mean rectangular parallelepiped, of course). The formulas were actually written out on the assignment sheet. I then asked my students to use the formulas to compute the volumes of some specified shapes. One of the shapes was a hemisphere.
I offered a plea of “no contest” to both charges. They were irrelevant. I patiently explained: “I have higher expectations of my students than merely plugging mindlessly into formulas. I want my students to think about what they're doing. This is not just a plug-in and grind class. Sorry.”
But not very.