Hi,
Well only marks don't matter. Also the thing that matters is that whether you are a localite or a outsider. They make a index with your marks and your hometown distance from the University and then gives you a hostel index according to which hostel is alloted. There are only 62 rooms for maths students in Ramakrishna hostel and that includes 126 students.
I hope my answer helps.
All the best.
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