## More math illiteracy August 20, 2009

Posted by lumixedia in General, math education, number theory.
Tags: ,

Just for fun, here’s a rather pointless anecdote.

My third-grade teacher decided to have a fun, hands-on activity to teach our class about primes. Now I have a low opinion of all fun, hands-on activities (give me a good, proper whiteboard lecture any day, and if you’re incapable of doing so you should really just work on improving your teaching skills before making me pay attention to you, and yes, this was my opinion even when I was very, very young) but that’s not the point of this post.

So first we got several copies of a 10×10 grid in which the numbers 1 through 100 were written in order. On the first copy, we colored in the numbers we’d say if we were counting by twos; on the next copy, we colored in the numbers we’d say if we were counting by threes; and so on and so forth up to tens. Then my teacher did the same thing, except on overhead copies of the grid. She then stacked all the overheads together, put them on the projector, and told us that the primes were the numbers that weren’t colored in on the screen.

The problem was, of course, simply that we’d colored in the entire top row, including 2, 3, 5, and 7. (No, I didn’t say anything at the time. I wasn’t that kind of kid.)

To cover up the pointlessness of this post, I will proceed to mention the Sieve of Eratosthenes, which is the correct version of the procedure we were attempting. Apparently it can be generalized to all kinds of cool number theory stuff too. Since I don’t really know much number theory, I will direct anyone who cares to Wikipedia or the impending awesome comment section.