Manhattan GMAT's Number properties guide is considered the best book in the market. I'm sure that it will help you a lot.

I second what papgust said. I greatly benefited from Manhattan GMAT.

Also be on the lookout for the number property problems people post here and see how the gurus explain the solution. I personally like Ian Stewart's way of explaining.

Thank you all! I wanted to use the Manhattan GMAT (have only heard rave reviews about it!) but since I was short of time I realized there wouldn't be much use of it. Therefore, I relied more on practice. Worked on a-z of quanti samples from the OG 12th edition, and several number property problems online, as many as possible, including beatthegmat and other available online resources. I have to say that it helped me have a much better grasp on the number property problems. I developed much more confidence and understanding to tackle this area of quanti.

From my experience, I'd suggest that all GMAT aspirants should PRACTICE, PRACTICE, PRACTICE. Nothing else can give you a better advantage to conquer the GMAT. I was pressed for time to get as much practice as I wanted to, but all those who have planned ahead well as well as those who haven't should be able to get the best through consistent practice. ANd yes, I didn't take any prep classes, though, and have been successful on my own at the GMAT! Thanks to all of you who have helped me with your posts once again.

Moving to GMAT Strategy!

But of course!