Indian Institute of Management Calcutta: Can one prepare for CAT/GRE on one's own without attending TIME or other such classes? ?

Definitely you can prepare without attending any coaching class. But I will say join some test series, because that will help in assessing your performance at regular interval. Further it will be good if you prepare for it with your friends. Group study will be quite helpful for CAT. Follow the link to know more about indian institute of management calcutta