Maths Spl

You can choose any subject of your choice. Studying with arts can also help you a lot for PC's.

No, you can take up BBA in IEM after completing your 12th if you had taken commerce stream in 12th and an aggregate of 55% and above.
Admission is through entrance test conducted by the university. If you want any further details about the universities let me know about your locality so that I can suggest a few good universities in your locality.

M.Sc maths is better in IIT Bhuvneshwar in terms of placement, faculty, infrastructure and ranking.

You can consider following colleges:
Brahmananda Keshab Chandra College - BKC
Jadavpur University
Jayasree Academy
JIS University
Lady Brabourne College
Netaji Subhas Open University
Techno India University
Vision Institute of Professional Study - VIPS

For doing BBA from this college mathematics is not mandatory.

Yes, you can do BA but if you want BA in economics or statistics then some colleges have made mathematics compulsory for it otherwise you can do BA in any subject.

You can do that but many colleges take maths as a compulsory subject for B.Sc CS. Check the requirements of the college you wish to go in.

The minimum eligibility criterion needed to be met for pursuing B.Sc in mathematics is a 10+2 or equivalent qualification in science or commerce stream with a minimum score of 50% in mathematics from a recognized educational board.

Go for Atma Ram Sanatam Dharma College. Nice crowd, upto the mark infra , go for it.