how rank is calculated in GATE?

Collage grades do not have anything to do with GATE rank.GATE ranks are purely decided by the exam you give for GATE . On this basis you will be called for interview different public sector industries such as NHPC ,BHEL,DRDO etc or you will get collages for M.tech studies Preparation of GATE papers is allowed to one of IITS and it totally depends on them what type of questions or difficulty they set far paper. You can prepare from previous year papers but you should not depend on them and prepare yourself well for every situation