1. I got sufficient number of questions correct in both sections, but in actual GMAT you need to get more questions correct.
2. I did not get sufficient number of questions correct.
Neither of the above - that's not how the scoring works. Unless you (a) scored VERY high or VERY low, or (b) ran out of time badly and had to guess on a ton or left questions blank, then you answered roughly 60% of the questions correctly. That's true at your 660 level, at 700, at 600, at 550... the score is not based on the # of questions you got right, but on the difficulty ratings of the specific questions that you answered correctly vs. incorrectly.
You can't simplify this to "I need to get this many right" and it's actually dangerous to do so, because it leads to decision-making that was appropriate when you were taking paper-based tests in school (which were graded based on percentage correct), but that same decision-making can actually be counterproductive on the GMAT.
I strongly suggest that you read the Scoring section of our free e-book The GMAT Uncovered Guide. It's really important to understand how the scoring works; otherwise, it's very tough to maximize your score.
with reasonable performance in top 15 in both sections
Are you referring to the first 15 questions in each section? It's a myth that the earlier questions in the section are worth more. Rather, your goal is to have a
steady performance across the entire section. Again, take a look at that Scoring section I mentioned above.
Please suggest me some good books for the same. I am planning to buy 8 books of MGMAT.
You are buying the books I would already have suggested. :) Although I will add: you scored in the 82nd percentile on quant, so you may actually benefit most at this point from our Advanced Quant book. It takes you through problem solving and analysis strategies that are necessary for 90th+ percentile scores on quant.
Re: DS, are you 100% sure that DS is actually a weakness for you? I ask because I see this scenario a lot: a student tells me that DS is a weakness, and that person also has timing problems on quant. I look at their tests (I can only do this for my students - sorry) and I see that they don't actually have a DS problem. Rather, they're spending too much time on PS problems and then they have to rush somehow to catch up, so they rush on DS... and then DS performance goes down. But they're not BAD at DS. They're just not spending enough time on it.
Use this article to review your latest MGMAT practice test and see:
http://www.manhattangmat.com/blog/index ... ice-tests/Note that the analysis described in that article is extensive - share all of your analysis results with us and we will be better able to advise you.
Also, I just updated the time management article - take a look:
http://www.manhattangmat.com/blog/index ... anagement/Finally, for RC, start with the articles I linked in one of my earlier posts, and then move on to the book when you get it. Also, start reading a little bit every day. Try these sites:
http://magazine.uchicago.edu/ - particularly articles in the "Investigations" tab
http://harvardmagazine.com/http://sciam.com/(Note: Scientific American can sometimes be a bit too casual compared to the GMAT, but if you don't like science passages, that's a good source to use.)