Hi Aspirant!

As per the marking scheme of JEE MAINS exam, +4 marks for each correct answer and -1 (1 mark will be deducted) for every wrong answer. So, as you said that you have attempted 50 questions out of which 35-40 are correct(35*4= 140 and 40*4 = 160) and 10-15 questions are not correct. So, your total becomes : 125-155.

You can check the marking scheme here:

https://engineering.careers360.com/articles/jee-main-exam-pattern

Now, for percentile criteria, I will be using previous years rcords, by which you can get 97 to 99 percentile, if you get marks between 125-155. However, kindly note that this is just a prediction which may vary depending on various factors.

https://engineering.careers360.com/articles/jee-main-marks-vs-percentile

Thankyou!