If you don't know what Khan Academy is, watch this. When it comes to GMAT prep, using Khan Academy can be a very effective tool for refreshing basic skills, but there's a catch. KA content is aligned to the common core state standards for math. The GMAT is NOT aligned to the common core.
Unless you know what you're doing, using KA will result in you learning a lot of math that you don't need to know for the GMAT, and not learning content that will help you in unanticipated ways. Don't get me wrong - I love math, and I love KA, and I highly recommend using it to learn all kinds of thing... after you get an awesome score on the GMAT.
I'm a coach on KA (something anyone can register for - not an official title) and most of my GMAT students are students on KA as well. That way, I can control what they learn and don't learn. Obviously, I can't do that for all of you, but I can give you a list of the common core standards that will appear on the GMAT:
First, you should register for an account on KA. Then, go to the common core map
Now, check out the attached pdf for a list of the standards you should work on. Keep in mind that you may already know a lot of this, but I'm trying to be as thorough as possible.
*** One more thing - there is some GMAT prep material on KA. Salman (Sal) Khan solves all the quant problems in the 11th OG in a series of 95 videos. Sal's a brilliant guy, but this isn't really test prep. His approach to almost all the problems is a frontal assault - none of the tricks and tactics that successful test takers use all the time. In addition, the 11th OG is hard to find, the videos are hard to navigate even if you have the 11th edition, and, finally, the guy behind GMAT QUANTUM (Mahendra Dabral), does the same thing much better - and with recent OG's. Check it out.
John L Easter
Founder: Owl Test Prep