What score are you looking for?
When do you need to take the GMAT by?
I would highly recommend (and confident you can increase your quant) if you get either the
MGMAT Math Foundations or Kaplan Math Workbook. If you have a bit more time, also get the
MGMAT Number properties
And regardless, get the GMAT Roadmap - it is an easy read book about the best practices for studying for the gmat - you can see my review in my signature.
Does this make sense?