IIM Ahmedabad - Indian Institute of Management Vastrapur Answered Questions

Since MBA is a masters degree, a bachelors degree is a prerequisite for studying at IIMs. Other than that you need to clear the bare minimum cutoffs of colleges which vary from institute to institute. Scores for IIMs vary from year to year. But a score above 97 percentile will get you calls from atleast new IIM's. The higher the percentile the better.
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For enhancing you Vocabulary go for Word Power Made Easy by Norman Lewis
It is brilliant book that helps you build a strong vocab. I would suggest you to buy this book and keep reading it again.
The book does not forces you to memorize any word, it explains the origin and history behind the word and hence making it easier to remember the words.
Know more on :
https://edudrona.com/questions/question/how-to-improve-my-vocabulary-and-spoken-english

IIM- Ahmedabad do not have a 0 fee admission. Students have to pay the complete course fee to study at IIM-A i.e. Rs 19.5 lakhs for 2016-2018 batch. IIM-A do have scholarships based on academic performance or financial status which subsidizes the course fees to some extent.

MBA in finance will give you a slight edge over others while grabbing initial concepts. While doing in marketing you will not get any such advantage. Choosing specialization should depend on your interest rather than expertise, because you can gain expertise with time, but your interest remains for long term.

You need to put some additional effort for VA section. For other sections i would suggest you to go through the basics in couple of months and start practicing questions. In case of VA, the basics of English, tenses, usage can be learnt from basic reading material provided by CAT prep books. After than i would suggest you to practice RC from readtheory.org where you can build you reading comprehension skills with time. After gaining a bare threshold, start giving mocks, analyze them and repeat till the D-Day.
All the best