Hi nikhil8384,
I'm sorry to hear that Test Day didn't go as well as planned. A 640/Q50 is still a solid Score though - although since you are interested in some highly-competitive Schools, you might need to improve on that Score a bit. When these types of score drops occur, the two likely "causes" involve either something that was unrealistic during practice or something that was surprising (or not accounted for) on Test Day. Before we discuss any of those potential issues though, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) How long have you studied? How many hours do you typically study each week?
2) What study materials have you used so far?
3) On what dates did you take EACH of your CATs/mocks and how did you score on EACH (including the Quant and Verbal Scaled Scores for EACH)?
Goals:
4) What is your overall goal score?
5) When are you planning to apply to School?
The process of applying to (and ultimately attending) Business School will require a big investment of time, money and energy on your part, so you really should make sure that the Programs that you apply to match your career goals/needs. There are a variety of factors that go into selecting the Schools that you'll apply to, so instead of just applying to Programs in which you might have a good chance to 'get in', here are some other things to think about:
1) Is there a particular company that you want to work for or industry that you want to work in? Certain degrees are more appropriate than others if you have a specific career goal.
2) What do you want your MBA to do for you?
3) Do you want to go to School full-time or part-time?
4) Are you willing to relocate? Are you comfortable with working through a program that is primarily online?
5) Are you going to be applying for scholarships?
Etc.
It's okay if you don't have answers to any of these questions just yet, but you really should try to define all of the important variables in terms of your goals, so that you can tailor your entire approach to getting into the best School that matches what you're looking for.
GMAT assassins aren't born, they're made,
Rich