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680 is a very good score! That's 80th percentile approximately
https://gmatclub.com/forum/gmat-scores-83890.htmlYou can check more here about how to figure out the score you need and steps to take further.
https://gmatclub.com/forum/brand-new-to ... 11381.html. Basically poke around the
decision tracker and see what people with your background were able to do:
https://gmatclub.com/forum/decision-tracker.html Also you can try to get a sense of your chances:
https://gmatclub.com/forum/what-are-my- ... 09854.htmlThe unfortunately reality is that as an Indian, you need the higher the better just to even get your application reviewed. Top 10 MBA programs likely looking at 750 and above for that specific demographic.
#2. You can boost your score 50-70 points likely with some review of mistakes but it is much harder to improve from 680 than 580 for example.
#3 Depends on where you want to go to school. I think if you are looking at an MBA in India, then I am not sure. I don't know enough about them. A high score may be a big help. In the US/Europe, you need career growth, salary growth, improvement, and a good brand name. This will not only help wtih admissions but also, more importantly, much more importantly with recruiting. In Europe and US it is very competitive to get a job and your former work experience (before the MBA) has a BIG impact on getting a job.