In terms of success ratio, CAT is one of the most competitive exams to crack for b-school admissions around the world. There are two ways of doing well in CAT.
- You already have strong fundamentals in quant (Mathematics, Logical Reasoning etc) and have decent spoken/written english which would mean its just a matter of brushing up fundamentals and practicing & getting used to the type of questions and the test environment.
- You dont have a strong quant background or are not comfortable with english grammer etc. In such a scenario, you would need to work much more on getting your fundamentals in place which can take a few months depending on your existing situation.
However, CAT is just one part of the puzzle. There is a bigger beast that comes after CAT which is the Group Discussion & Personal Interview rounds which test much more than just your aptitude. The second stage is not something you would be able to cross by just preparing for a couple of months after the CAT results hence my recommendation would be to start preparing for both rounds simultaneously. Given that a large percentage of CAT aspirants are engineers, quant seems to be less of a problem for them but they end up putting a lot of extra time and effort on verbal and it always helps to read a lot!