My other project this summer, as I mentioned briefly before, is to re-learn Calculus 1 and 2 (as they are normally broken down into courses). So far I've spent about 8 hours on this, and I plan to keep going basically all summer.
I took Calculus 1 my senior year in high school (1991-1992), which I think was when I hit my mathematical peak. I took Calc 2 at Rice the next year. Needless to say, it's hard to remember much from 13 or 14 years ago.
A few years ago, when I was still in Houston (so this would be about 7 years ago), I re-took Calculus I at HCC because I was considering being a math major and realized I should probably actually know some math before trying to go learn some more math. What I found I had mostly forgotten was not calculus per se, but the algebra needed to do the calculus.
I need to know this calculus stuff because both of my fall courses rely on it - I'm taking Calculus 3 and a calculus-based Probability and Statistics class. So it seems pretty scary to show up with 7- and 14-year-old vaguely recalled math knowledge.
I bought a big calculus textbook and a graphing calculator (the TI-86 - sorry to all you HP fans) and some other paraphernalia, and these things live in a clear plastic box in the living room, so that when I sit down to do it, everything is in one place and it's very easy.
And once again I am finding that the calculus itself is not difficult, but what I'm having trouble with is algebraic techniques that I've forgotten or am very rusty at - things like factoring polynomials, rationalizing denominators, and converting trig functions into each other. I was proud of myself last night when, at the moment I needed it, I remembered that there was such a thing as the "quadratic formula" and was able to look it up in the reference part of the textbook and use it. But I know there are a ton of other techniques that I used to know and that I do not know now. Sometimes they show up in the examples in the text, and sometimes not.
Every time I sit down to do this, I read the relevant part of the book, and then do some of the exercises (the odd-numbered ones, so I can check my answers in the back). I've run into a few that I can't solve (due, I think, to lacking some technique or other). I expect to post them to Google Answers at some point to get some hints.