How much do I need to score in the CAT to get a call from IIM Shillong if my academics are all 70%?

IIM Shillong’s eligibility criteria are

• a bachelor's degree of minimum 3 years duration
• 80% marks in 10 and 12

No or very little weightage is given to graduation marks so you are likely to be eliminated owing to your low marks in 10th and 12th.

Still, I have mentioned the CAT cutoff for the General Category.

The CAT cutoff for IIM Shillong's GD-PI round is 75 percentile for candidates belonging to the General and EWS categories. For candidates belonging to DA and ST categories, the minimum CAT cutoff is 50 percentile, and for those belonging SC category, the CAT cutoff is 60 percentile.