Hello Priyanshu,  40 days are enough to score 250+ marks in n Jee main,  if you are derivative at your work. Rest of the part will become easy for you if you will do study with positive mind.
So first of all make list of important topics , Because days left are really less,  so first study those topics which are important and then go for remaining. Clear your concepts,  never mug it,  try to watch video lectures to clear your concept and doubts.  Best practices is to solve question papers by setting time.
On careees360 necessary study material is available,  So you can make use of these also.
I hope it will help you more.
Thanks.

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