Dear aspirant,

According to your question,to clear the NDA exam one has to just stick to the basics and keep their concepts crystal clear. If they would follow ncert syllabus properly then it would be much easier to get the exam. You should follow a proper work plan and strategy to get hold of the pattern of the exam.

Coming to your second part of the question this is absolutely ridiculous that if you sleep less and study more you will clear the exam. You have to sleep for atleast 7 hrs of sound sleep.