## Thursday, November 22, 2012

### Here’s a tip

I usually end up doing some math to make the total amount nice and round, but this guy skipped the middle man.  So kids, was this a decent tip?

found on failblog.

## Sunday, November 18, 2012

### Have you noticed this?

Look at the number of characters... do you think this happens for any other sum?  Maybe a product?

## Wednesday, November 7, 2012

### Fractal mountains

Driving home yesterday I found myself admiring the Olympic mountains and wondering about the simplest way to model them.  Here’s a start (click the image if you have Java installed).

I used a sequence of coin flips and the rule “Heads, go up, tails, go down”.  So a string of coin flips HTHHT would be translated into UP-DOWN-UP-UP-DOWN, and look like this:

To give the illusion of depth I increased the step length and darkness the farther down the screen you click.

Fractal mountain ranges and landscapes are used all the time in movies and video games, since they’re so easy to make and look just like the real thing.

## Thursday, November 1, 2012

### Teacher fail

Recently this was posted in an email group:

A former student has e-mailed me that his current teacher marked wrong his interpretation that the origin is NOT located in any Quadrant.  This teacher told him that the origin is in all Quadrants.
I'd love to hear some of your takes on this.  I've pretty much tell my students that points in the coordinate plane can be classified in 7 positions - one of the quadrants, on an x- or y-axis, or at the origin.

I knew when my hackles raised that I should hold off on responding, but luckily Illinois teacher Paul Karafiol did the job for me:

On the pedantic side, "in" a quadrant means in the interior, which would clearly exclude the axes under the standard (metric/topological) definition of interior.  Whether we decide that those axes are parts of the quadrants (though not the interior) or are "special" is a different matter.  I could imagine this making for an interesting class discussion that would touch on big mathematical themes:  why we try to avoid making arbitrary distinctions (a reason for calling the axes special, rather than assigning them to quadrants), the importance of precise definitions, etc.  What I can't imagine is this making for a good reason to take a point off a test, especially in the absence of such a discussion.  What well-defined learning objective is it related to?  Why is this an important part of what students should know or be expected to do?  Why take this opportunity to reinforce kids' basic idea that math is about learning a set of arbitrary rules, especially when--as might have happened here--"learning" is really code for "divining by esp, ornithromancy, or whatever"?  (I'm not even raising--except in this parenthetical--the whole idea of "losing points" versus raising points, or the really awesome article I just read about other "toxic" grading practices:  http://www.ascd.org/publications/educational-leadership/feb08/vol65/num05/Effective-Grading-Practices.aspx)

Incidentally, the original teacher in this story may want to check out Paul’s diatribe on another stupid grading practice.