<p>I took the GREs about 15 years ago and bought a basic review book (Princeton Review? College Board?) to prep ... mostly to get a handle on the types of questions that would be on the test and what the best strategy was (should I guess, etc) ... 2-3 hours of prep at most. This approach worked fine for me (same basic approach for the SATs also).</p>
<p>Ack. If you really mean the GRE math SUBJECT TEST (as opposed to the general GRE math section) it's more than basic calculus -- much more. I gather this is kinda too late for the original discussion. But I just took it a few days ago and it includes math through multivariable calculus, linear algebra, number theory, topology, and some advanced analysis. Not a lot of anything in particular, but you have to be pretty sharp to do well... so a warning to anyone who wants to take the GRE math subject test to prove their skills, don't do it unless you have at least a few years of college math under your belt.</p>