Do not be fooled by that book (Kaplan Foundations), it is utterly useless! I purchased one thinking that once I understood the concepts of the subjects covered in the GMAT exam, everything else would be a breeze. Well, that was a waste of time.
I decided to take a practice test to see if I understood the concepts better...I can't even type the score I got out of embarrassment. Which was what led me to this website; I decided to find out what books other people were studying, most mention MGMAT. So I changed my GMAT date and I purchased the 5 Quant books MGMAT had to offer. Since I work 9-5/6 every weekday, I dedicated 7-10.30 pm on weekdays at the local Barnes and Noble store and spent 3pm-10.30pm on weekends going through each topic covered. At the end of book 3, I decided to measure how better improved I was, and I pretty much doubled my score to 630 after 1 month of rigorous studying.
I have my GMAT in a week, and I still need to completely cover Geometry and Word Translations (both my greatest weaknesses), and I must say that even with been clueless when it comes to many word problems and geometrical questions, scoring 630 was great for me (and I believed I may have danced around the store when my score was revealed)
I plan to take another test tomorrow morning, hopefully, my score would have increase dramatically again.
Anyway, if you have problems with Quant, buy the Manhattan GMAT books, and you'll see an improvement, if you put the hard work into it.