MAT is Management Aptitude Test which is conducted by AIMA. The score of MAT exam is not widely accepted by Top Bschool. The exam is not that useful for MBA program from top Bschool.Total 200Qstn with +1,-0.25 marking with 5sections.
CMAT is Common Management Aptitude Test conducted by AICTE. It wilk be on Jan-2019.Score of CMAT exam is used by some reputated top Bschool likw KJ Somaiya, Welingkar ,Great Lakes , SIES, etc.Exam is of 100question with 25Qstn from QA,VA,LR,GK respectively with +4,-1 marking.
CAT is conducted by IIM. Every year different IIM Institute conduct CAT. Paper pattern is QA,DI-LR,VA-RC with 34,32,34 questions in each section respectively. Marking pattern is +3,-1 and total 100marks. Difficulty level of exam is also high and o e of toughest exam in India.All Top Bscholl( Except-ISB) consider CAT score.
CAT EXAM SCORE IS ONLY CONSIDERED BY ALL IIM'S AND ALL TOP BSCHOOL IN INDIA.
Hope it clears your doubt.
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They are different exams to get into different colleges.
Basically cat is accepted by most of the colleges and mat, cmat is accepted in selective colleges.
Hope it helped u