Books to study for Math GRE, self-study, have some time.

Solution 1:

The Math Subject GRE is 50% Calc 1, 2, 3, and Differential Equations. High school algebra and linear algebra are another 15-20% probably. If you do well on just those questions, you will be in the 70th or 80th percentile. Note, this is compared to students wanting to study math at graduate school, so this is very good. Learning several entirely new subject will take months, probably more time than you have, and will end up adding just a few points to your score. Mastering the subjects you have already had will help your score much more.

Here is a link to a previous test, including the breakdown of subjects.

http://www.ets.org/Media/Tests/GRE/pdf/Math.pdf

Note 25% is "Additional Topics". You'd need to learn several semester courses worth of material to get this stuff. Don't worry about that.

Solution 2:

I took it last year. Make sure you are an expert at calculus. The higher level questions are very easy. For example one question on mine was which of these sets is not a group under multiplication, the one that failed didn't have inverses... I tried to study a little of everything and wished I just studied tons of calculus and linear algebra.

Good luck. Oh also, when you take the test keep in mind that you do not need to answer every question to get a very good score. Check out past scores and the rules for scoring before you take the test. So you don't feel overwhelmed during it.