Dear Shubham, there are 20 IIMS. And if you belong to SC Category, you will need to score atleast 60-75 percentile in CAT because each IIM has its own selection critera. Top IIMs like Ahmedabad, Bangalore, Calcutta, Indire, Lucknow etc will need a minimum of 75 percentile and new IIMs will need atleast 70% for your Category.Now, because IIMs also look into your Academic profile, Diversity factor, course in which you completed your Graduation and work experience, you might lose out on few points as BCA is a regular course and you do not have work experience. So to be shortlisted for IIMs, you should score higher on CAT to balance your lack of work experience and normal BCA degree. Then you have to perform real good in WAT and PI rounds. But to be shortlisted for IIMs, your target shoud be atleast 80-85 percentile. Now that takes care of 20 IIMs. And for the top B schools, it should be atleast 75 percentile.