hi,

to admission in banaras hindu university post graduate courses, you have to appear in bhu pet, i.e post graduate entrance test. however the questions would be based on your undergraduate courses syllabus, i.e study the full b.sc in mathematics syllabus , you may follow some books which have previous years papers to get some suggestion of questions difficulty level. follow the below link to get old question paper: http://bhuonline.in/old-qus-paper-2019.html

some of the book you may follow is mentioned below:

MSC MATHEMATICS ENTRANCE EXAMINATION by ANSHUL JAIN & SUBHASH JAIN (Author)

MSc Mathematics Entrance Examination  (English, Paperback, Rashmi Gupta, Suraj Singh)