You must be aware of the way marking scheme of BIT, Mesra works. In case you have forgotten let me remind you.
Mid Sems: The question is worth 36 marks and you can attempt all. You can get a maximum of 30 marks.
End Sems: You get questions for 94 marks and you can attempt questions for 70 marks.
The sum of both is taken and then the grades are given. 50-59 marks get you a B which means a 6 on scale of 10, 60-69 marks mean B+ which mean 7 on grade of 10. If that is not enough you have to add 6% to quote your percentage when you convert to percentages.
Say you get 18 in your mid sems(50% of total) then you need just 42 in the end sems to claim 75 percentage. But 42 is not half of 70, I hear you say. Well, but then you get two extra questions, worth 28 marks to leave. And I will claim that if you are getting 42 then you donot know at least one of those two questions. So you get 42 of 84( again half), your sum is 60, which means a B or 7/10 grade, which means 76%.
And then you say that Bit management hates you!