I've yet to run into anything at the table that requires me to do much math other than divide #'s. I don't ever really bother to convert anything to percentages, I find odds easier to work with mentally anyway. I'm kind of in a similar boat as you though, I didn't bother to learn much math when I was in school. The math I know, I know well, but since I didn't take any higher level math courses some of the math I run into away from the table can be confusing (probabilities and such).
I tried refreshing and learning using the net and books and whatnot and found it more frustrating than anything. I gave up and decided to go back to school since many of the things that interest me are pretty math heavy (physics, economics, etc). Figured it'd be a bit easier that way, and it'll be useful to me in many areas.
Along the way I did run across a couple of books that have helped alot while at the table.
link
I've found the tricks they give in this book to pretty useful for rapidly calculating in your head. Might be kind of what your looking for.