Marks on a bell curve

UofA

New Member
#1
Hello,
Just wondering,
Most of my exams are graded on a bell curve and sometimes after an exam is handed back to me and the prof writes on the blackboard the class average, number of people participating in the exam, and along with the standard deviation of the exam mark distribution-- i see people using those numbers to find out exactly what their grade is, relative to the class; Regardless of what they actually got.
Can someone tell me what those people are doing to find out what their grade is or how they know in what percentile they are in, relative to the class.

Thanks
 
#2
Hi UofA,

You can calculate the z-score first and then loook up the percentile in the normal table.

z-score = (grade-mean)/sd

For example if the z-score is 1.28, the probability from the normal table would be 0.8997, thus your relative standing is 90%.