CAT exam is not the only criteria for selection in IIMs. Some one can get a call from IIM Ahmedabad at 90 percentile as well depending on the academic background. Also, someone can get rejected at 99.9 percentile as well!
Here is a video explaining the shortlisting and selection criteria for IIM Ahmedabad and IIM Bangalore
My Background:
I appeared for CAT twice. In 2017 I scored 99.21 percentile where I only had call from Indore among the BLACKI and scored 99.91 percentile in CAT 2018 where I had call from all IIMs except IIM Bangalore. I managed to convert all calls in 2018 and joined IIM Ahmedabad for the 19-21 batch!
