Deficiencies

Subtraction:

Yesterday I was at Target, and I bought $14.77 worth of stuff. I gave the clerk $20.02, but he mis-keyed $200.25. It took us way longer than it should have for us to figure out how much change I was supposed to get. I can not subtract in my head.

Newton's Method:

I know it has something to do with finding the zeros of functions. I think that there is a recursive component to it and that someone at Cornell once wrote something about how it relates to chaos/fractals. That's about all I know. In a few weeks I'll be teaching it.

Linear Algebra:

So often I'll be reading something and I won't get it, and then I'll realize: it's because I don't know as much linear algebra as I should. I'll have to teach it sometime.