Science

For M.Sc, there is something called JAM exam.
You can get more information here:
http://jam.iitm.ac.in/jam2016/ac
The candidates who qualify JAM 2016 shall have to fulfil the following eligibility requirement (ER) for admissions in IISc and IITs. All candidates admitted through JAM should have a Bachelor's degree. At least 55% aggregate marks, without rounding off, (taking into account all subjects, including languages and subsidiaries, all years combined) for General/OBC-NCL category candidates and at least 50% aggregate marks, without rounding off, (taking into account all subjects, including languages and subsidiaries, all years combined) for SC/ST and PwD category candidates
in the qualifying degree. For candidates with letter grades/CGPA (instead of a percentage of marks), the equivalence in percentage of marks will be decided by the admitting institute (s).

If you have decided to opt for Maths (Hons) just because you are passionate about the mathematics which you study at 12th level, then my friend, I think you should think about it once more. This course is quite different from what students expect it to be. Generally, students get attracted towards calculus which they study at school but in this course, differentiation, integration and almost all the subjects which you study at 12th level are rarely studied. Honours in mathematics at DU almost comprises of studying Pure Mathematics which involves the subjects like Analysis, Group Theory, etc., which are generally unheard till class 12th. Pure Mathematics is very less about calculations and more about theory and proofs. It's less about cramming those formulas and more about understanding the stuff. If you are interested in having deep knowledge about mathematics, want to know the reasons behind all what you have studied till now and are ready to begin a new theoretical journey of mathematics, then this course is undoubtedly meant for you. Teachers at DU are excellent in their respective fields and you will be able to get a very deep understanding of the subjects. One thing I can assure you, a mathematics student of DU is far better than a mathematics student of any other university since many subjects taught here are only taught at post graduation level in other universities. I will highly recommend you to at least once go through the syllabus of DU before enrolling your name for this course.