please mention the college name. Generally, some college select the caniddates through entrance exam or some through the merit. The minimum eligibility criteria for the MSc Mathematics course is student should have passed B.Sc. (Mathematics) or B.Sc. (Mathematics with Computer Science Applications) or any other relevant degree with Mathematics and English as main subjects with a minimum of 60% marks. The minimum percentage varies from University to University. Some institutes also consider the B.Tech and B.E candidates.
You didn't mentioned which colleges you are talking about. So I would recommend you to get back to career360.com (//career360.com) with more specific regarding to your question so that we can provide you the information you want.
Have a great eve!