I'm not a stellar math student, either, so I know where you're coming from. The test just covers the very basics of algebra, however, I was given a series of graphs and asked which one was a function, so you may want to brush up on the "vertical line test" and such. Any book that thoroughly covers PEMDAS, absolute value, fractions, exponents and factoring polynomials should be a tremendous help.
If you're extremely weak in algebra like I was, and can afford the option, you may find a private tutor more helpful than a book. I ended up hiring a tutor after getting 11/20 on my placement exam, and ended up passing it the next time around. Obviously not everyone can do that, but if you know you need more than a little math help it may be a good idea. Either way, a book or a tutor is bound to help you out.
Welcome to the Columbia postbac family. 🙂
