Hi Aspirant,
The minimum marks to be eligible for CAT is 50% in your graduation.
However,if you want to go through MAT or XAT, there isn't any minimum requirement.
Also,in some places,the minimum requirement for maths/statistics is around 60.
Try to score high in your graduation as it may also prove to be an important factor in your selection.
Also,try to score high in your entrance exams for getting into your desired B-School.
Hope this helps.