GMAT

The GMAT score qualifies you for a foreign institution, whereas the CAT exam is required for admission to the top Indian Institute of Management. It is challenging but not impossible to prepare for both exams. You can follow the experts' suggestions to prepare for both exams:
1. Find common sections to study in both exams. For example, the reasoning and quant sections are asked in both exams. You can practice these simultaneously.
2. You can also allot a separate time slot to analytical writing, which you can pair with the reading comprehension section of the CAT exam.
3. Understand the different demands of both exams to prepare accordingly. The GMAT prioritizes the verbal section, whereas the CAT prioritizes the quantitative section.
4. Select your study material in such a manner that it has some common books or notes that can be useful in both exams.
5. Give mock tests for both exams on alternate days. For example, if you are giving a GMAT mock on Monday, you should give a CAT mock on Wednesday. Because the GMAT takes significantly less time than the CAT you can begin preparing for the CAT before the GMAT. Also, make sure you leave enough time between the two exams to deal with exam stress.

It is not the only determining factor and a person with high CGPA has better chances of getting into in good colleges or company is not very true and is situation specific, I would elaborate this with some examples. As far as placements are concerned you need to score above a particular range (ex. 8 CPI and above for some companies) to appear for the process. As far as getting in a college for higher studies is concerned, it all depends on university and your overall profile. Again, for example if you have done some phenomenal research and published lots of material, you have given some TED talk and you are applying to IVY league University where you want to extend this research definitely, they are not going to underestimate you just because you have low CGPA. But definitely in certain scenarios it is high CGPA which at least gives you an opportunity in campus placements. Again, for example Mercedes Benz usually short lists top 5 students from each college (based on CGPA or aggregate %) and invites them for the recruitment process in their campus. Thus, if you don't stand in those top 5 no matter how much practical experience you have got, you can't even attend the interview process.