Hi Pratik!

every competitve exams has its own seperate sectional cut-off and in order to qualify one has to pass through all the cut-offs. 

Apart from this there is a minimum marks below which one cannot qualify and has no connection with the sepearte sectional cut off. For example the cut off for PCM is 30 each but for the overall qualification it requires 100. So accordingly one has to prepare for the paper.

hope this answers your query, all the best

cheers!