Maths Spl

It will depend on institutions. Information related to the admission procedure is available on the college website.For more details, you can refer the below mentioned link:
https://www.shiksha.com/science/course/b-sc-in-mathematics-jadavpur-university-jadavpur-kolkata-273121

The eligibility criteria of DSSSB TGT Maths is given below.
1. Educational qualifications : A Bachelors Degree or equivalent with at least 45% marks from recognised University in the concerned subject.
2. B.Ed. From a recognised university
3. Pass in the Central Teacher Eligibility Test (CTET)
So from above CTET is mandatory for DSSSB TGT.

You have to opt for National Institute of open schooling (NIOS). Here you can do the class 12th with Maths and Science as per your needs. However you can not change your stream during the current academic session.

Since you have statistics of all three years, you can apply for M.Sc. Statistics. Aggregate marks are 50% overall and 60% in statistics in your graduation.

I think you should go with B.Sc. Statistics, because B.Sc. Data Science students have big competition with B.Tech CSE students and most of the companies prefers to select the B.Tech CSE students in place of B.Sc. Students.

For doing BBA after class 12th, maths is not compulsory. Eligibility says 10+2 in any discipline. There are many colleges that offer BBA like SP Jain in the western part of India and if you are looking for Delhi NCR then colleges of DU, IP and IILM University Gurugram are the options that are available.