You should first start with economics, then go for accounts, law and Maths respectively
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Economics- This subject depends totally on interest factor, so develop a liking towards this subject
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Accounts- Its very easy, If you havent studied accounts earliar, I will advice you to buy P.C tulsians book
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Law- The book is very small, but questions can get tricky...MCQs behind every chapter should be at the tip of your finger
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Maths- It all depends on you, if you are good in maths, well and good,..if not you should at least study the mathematics part of it if not statisitics
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I was 10+2(PCM) student, still managed to crack it with very less study.
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As far as rank is concerned, it is more difficult to get a rank in CPT then later stages of CA course because portion is very easy and candidates are more. In other stages rank depends on hard work you put in.
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For Cracking CPT, more then confident , control of over confident is required..Just dont get carried away by those thin books
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Good Luck