It depends on the top 10% highest marks...then they take out their mean and further take the 10% of the mean which will decide the percentage fr the A grade...
in stats lets consider that the top 10% marks lie between 180-190 (90%-95%)...take the mean of it and it'll be 92.5%...multiply it with 10/100 and answer u get is 9.25...now subtract this from 92.5 and u'll get 83.25%...this is the lowest of the percentage on which u'll get an A grade...
this method will be applicable from this OCT/NOV '09 session...
this i have been hearing from some of my senior teachers...i don't knw whether this method is rite or wrong but if its wrong plz do lemme know...CHEERS!!