What should I do for the preparation of CAT (MBA, IIM)? I'm a 12th passed?

The students who wants to get admission into the MBA course must obtain minimum 50% in their UG degree. They have to appear for any one of the national level entrance exams for MBA course admissions such as CAT, MAT, XAT, CMAT, MAH-CET and ATMA exam. The minimum cutoff required in CAT exam is 50%. I

Students may get admission in IIM Bangalore with 95 percentile in CAT. But this is not enough to get a seat. The admission chances also depend on student's overall profile. This includes academic scores + performance in the selection rounds. Students can check the cutoff trends to know better.

IM selection criteria includes Written Ability Test (WAT) and Personal Interview (PI). Academic record and work experience are also taken into consideration for final selection.

To get 99 percentile and above, candidates must attempt 40-45 out of 68 questions in CAT, with maximum accuracy.  

Yes, six months are enough to prepare for CAT exam, if you can dedicate 8-10 hours to it daily. In the first three months complete the syllabus. In the last three months practice mock tests and do revision.