Thank you very much for your answer. Now I want to know whether the preparatory course is ussful or not. Also , please share the success percentage of preparatory course. How many of those who studied this preparatory course got seats in IITs and how many didn't. Please do share because your advise will be very useful for me.

Koushika Moka Hello,
I'm glad my answer helped you. As for your dilemma, the preparatory course is only worth it if you put in excess hardwork. The course that goes on for a year heavily prepares you for a seat in IIT or prestigious B.TECH colleges. So its alot of hardwork and if older trends are to be followed, the final paper of the preparatory course is said to be harder than the actual IIT paper. Please don't get me wrong, I'm not trying to scare you, I'm simply answering you with all honesty.
As for success rates, many students have gotten into IIT after this course and it depends heavily on your ranks. Ranks in the top 100 are needed for that.

Rest assured, if you do the course with due diligence you shall surely succeed.

Good luck!!