Exam

If they didn't ask for two decimal places, then your answer is correct.

Your marks should be around 300-320, means your rank should be under 150 in general category.

If you want CS in IIT Delhi then your rank should be under 200 for that you should get at least 300 marks in JEE Advance.
If you want mechanical, electrical, civil then closing rank would be around 800.
Although, there are various branches in IIT Delhi , so closing rank would around 3000-4000.

If you are a general candidate, then you should be under 200. For this, you should get at least 290-300 marks out of 372 in JEE Advance.

Three is also correct, but more precise is 3.00. I think this will not be wrong.

Eligibility for VIT Architecture Course is Candidates must have a valid Score, in the National Aptitude Test in Architecture (NATA) conducted by Council of Architecture (COA), India / Candidates who have qualified NATA. The eligibility and selection process considering the NATA score will be subject to any changes that NATA / COA (Council of Architecture) may propose for institutions to follow, in the current Academic year. So there is a much chance of getting a seat in VIT Architecture.

Yes, BCA is best at VIT University. We can't predict the placement in BCA, as it mainly depends on the recruiter preference. VIT is well known for its placements record.

There are many entrance exam which will open up for top b-schools like CAT, XAT, MAT, ATMA, CMAT, MAH, CET, TISSNET etc.

Kindly predict your college in this college predictor. JEE Main rank predictor is an online tool which predicts the candidates rank range and probable colleges based on the difficulty level of the examination, average marks scored in JEE Main and seats available in IITs, NITs, GFTIs, and other SFTIs. The rank predicted might not be accurate but it certainly does give an idea to the aspirant. Know your college admission chances based on your JEE Main Rank, Home State, Caste, Gender, etc. Here https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor