How much minimum marks needed in mains and cbse board 12.

It all depends upon your caste category and cutoff of that year. If you are from general category then its around 100-105 marks needed to clear cut off.

Your class 11 and 12 aggregate should be above 75%
And jee main score above the cut off which will be released after jee main score. If we predict, the score is around 105-110.

The minimum marks for jee changes year to year. As the jee cutoff marks is decided based on following:

Total number of candidates appeared for the exam

Level of difficulty of exam

Previous years cutoff trends

Number of available seats

Overall performance of the candidate.

The cut off for jee general category 2015is 115
The cut off for jee general category 2016 is 100
The cut off for jee general category 2017 is 81

So as u see the cutoff varies from year to year for all categories of the students.

Coming to cbse board you must secure at least 75% aggregate marks in the class 12 (or equivalent) board examination.

All the best prepare well for your examinations.