Best GMAT Math book

I would go through the MGMAT questions which are very usefull to brush up the quant fundamentals. Afterwards, if you need a reference book to quickly look up some formulas or rules I would recommend you to use the GMAT CLUB MATH book as a reference source.

Don't be too quick to dismiss the OG. It's the only published source of real GMAT material, so it's the one book that everyone must have, regardless of how they prepare! Of course, it isn't an instructional book, so you'll also need something to guide you through the material. Naturally I'll recommend MGMAT.

Here's what I wrote when someone made a similar request a few months ago (gmat-quant-advice-172223.html):

This is a common request, but I think the OG is a better resource than most people give it credit for. Certainly if you are performing at a very high level in quant, you will find many of the OG problems fairly easy. However, this does not mean you shouldn't spend many hours working through it. First, it is highly representative of the style and content of the questions you'll see on the GMAT. Second, it *does* contain quite a few very difficult problems. Third, in order to hit a high score in quant, it is important to be *very* accurate on the lower-level problems.

So I recommend that you spend plenty of time working through the OG in timed sets. You can push the time a little faster if you're really finding the problems easy. Then you should spend lots of time reviewing your work and looking for ways to work more efficiently and reduce your error rate.

If after all that you still need a source of more difficult material, I humbly suggest our Advanced GMAT Quant strategy guide.