Maths

No, If you have to do engineering then Maths must be there in any branch of engineering.

70-80% of marks were required for admission into bsc nizam college

70-80% marks were required in bsc from any recognised University

Crack any net exams line csir UGC etc. With that qualification one can get admission into Ph.D. by consulting professors in universities or institutions.

Ranchi University admission is conducted in both online and offline modes. In case of online admission process, candidates are required to fill the application form available on the official website of the University. For offline admission, candidates need to visit the campus to purchase and submit the form in-person. The University offers admission both on the basis of a valid score in a course-specific entrance exam and based on a valid score in the last qualifying exam.
For mathematics program admission is based on previous undergraduate Bsc merit.

Yes in every online exam Conducted by an central or state institutions extra paper for rough work is provided. Here in CTET conducted by NCTE rough sheet also provided for Maths.

Chinmaya Mission College, Talap was established by the great visionary; His Holiness Swami Chinmayanandaji, in 1975. Like any other Chinmaya Educational Institution, this College also offers "EDUCATION WITH A DIFFERENCE" through Chinmaya Vision Programme which integrates the best in our culture and philosophy with Academics. Fees structure for BSc Mathematics is as -
For first year -
ADMISSION FEE - 500
TUITION FEE - 16600
CAUTION DEPOSIT
(Refundable after completion of course - 1500) For 2nd year
Admission fees - 500
Tuition fees - 10300
CAUTION DEPOSIT
(Refundable after completion of course - 1500)
For final year
Only tuition fees - 8300

The candidates must have qualified their BSc/ BSc (Hons) or equivalent degree with Mathematics as a regular subject. The applicant must have secured a minimum of 50% (47.50% for SC/PH) marks in aggregate.it is the common mark for Msc for all colleges

As per your marks it seems that you have score 75% so your definitely eligible for the JEEMains and if you score well in JEE Mains then you can definitely get admission in good college. And if you score is best in the JEE Mains then you can also get change to give JEE Advanced.