You don't get college in the basis of your 12th marks. First of all you need to do graduation in any stream as MBA is a post graduation degree.

Then after that you need to appear in at least one of the MBA exam exams like CAT, XAT, CMAT, CAT etc. After this in all the colleges you have applied will make up a merit list to call students for next round of interview and WSAT which is based on your aggregate score which comprises of many factors such as CAT marks, 10th 12th and graduation percentage, work experience, engineer or non engineer with different weightages for different colleges. In this your academic records have around 10-20% weight and MBA exam marks have maximum weight of 35-70%.

After this you go through second round and then again a final merit list is made including interview and WSAT marks which along with MBA exam marks have maximum weight in the final merit list. This is used to give admission.

With your 70-80% in 12th class which is average performance you need to score a high percentile in MBA exams.