DU JAT

Nope brother.
65% weightage for DU JAT and 35% for board exams.

You must have maths in 12th. The minimum marks eligibility is 60%.

You should download PDFs and study monthly and weekly current affairs and business affairs of last 6-8 months.

No, you can't admission in SSCBS for BBA because for getting admission there you should have above 75% in your 12th class without this you can't get admission there.
Good luck!!

Please check for your eligibility to appear for the DU JAT from the criteria mentioned at the link provided below:
https://www.shiksha.com/university/university-of-Delhi/exams/du-jat.

https://www.shiksha.com/university/university-of-Delhi/exams/du-jat
Kindly refer to this link for a detailed information about the exam and everything else related to it. I hope it helps.

DU JAT Question & Sample Papers 2018:
Download previous year question papers and sample papers of DU JAT 2018 for your exam practice at the link provided below. You can download all last years' DU JAT exam question papers and sample papers free of cost. You can also download preparation guides for DU JAT designed by Shiksha experts. https://www.shiksha.com/university/university-of-delhi/exams/du-jat/question-papers.

Yes u can write.

Please check for your eligibility to appear for the DU JAT exam from the criteria mentioned at the link provided below:
https://www.shiksha.com/university/university-of-Delhi/exams/du-jat.

Check out this link for detailed information regarding DU JAT and exam date:
https://www.google.co.in/amp/s/www.shiksha.com/university/university-of-Delhi/exams/amp/du-jat