Hi bssb.

Fortunately the GMAT does not use all that many quant concepts. The point of GMAT is to test your skill in getting to answers more than to test your knowledge of math itself. So really you just need to understand a few dozen basic things.

Much of what you need to do is to assess what you understand and what you don't understand and what you could understand better. Then go over each topic, checking off one and moving to the next, maybe going back to some topics later for more review. When you do things that way, the whole process is pretty manageable. You whittle away at the stuff you don't know, and the to do list gets smaller and smaller.

Once you understand the basics involved in a question type and have some idea of how to get to the answers to that type, you can do dozens such questions until you become an expert. Trust me. You can do this. I have seen people who felt intimidated by GMAT quant drive their scores up this way. Takes work, yup. Still, getting your score to what you want it to be is eminently doable.

For categorized quant practice questions you could see how you like the question bank here. https://bellcurves.com To access it, you go to the GMAT area of the site and sign up for a practice account.