Hi anirbandeep2907,
I'm sorry to hear that Test Day didn't go as well as planned - although a 640/Q47 is still a solid Score (and it might be enough to get you into your first-choice School). 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) On what date did you take the Official GMAT?
2) How long have you studied in total? How many hours do you typically study each week?
3) What study materials have you used so far? What “brands” of CATs/mocks have you used?
4) Have you taken any other CATs/mocks besides the 4 that you listed? On what dates (or approximate 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:
5) What is your overall goal score?
6) When are you planning to apply to Business School and what Schools are you planning to apply to?
While the ESR doesn’t provide a lot of information, there are usually a few data points that we can use to define what went wrong on Test Day (and what you should work on to score higher). Since you purchased the ESR, I'll be happy to analyze it for you (and you can feel free to PM or email it directly to me if you'd prefer to not post it publicly).
GMAT assassins aren't born, they're made,
Rich
Contact Rich at: Rich.C@empowergmat.com