let me explain the whole thing:-

In relative grading system the grades A,B,C... are given according to % of top students, % of middle students or % of rest students etc. For example:- If i decide a relative grading like top 20% students should be graded "A", middle 20% students "B" and rest as "C" . If the strength of the whole class is :- 100 then top 20 will get "A", next 20 will get "B" and rest will get "C". Now, suppose the professors have decided the above grading system. If the questions in the exam were very tough then it may happen so that the top 20 students may have % scores like this:-

95, 90, 85, 80, 77, 72, 67, 60, 58, 57, 54, 50, 49, 48, 47, 45, 44, 42, 40, 35......

then all the above students are graded "A". Is it not funny????? person who got 35% is "A" graded and person who got 95% is also "A" graded. It all happened due to wrong assumption. If the assumption of "A" grade had been top 5% students then the "A" graded students wud have been :-

95, 90, 85, 80, 77