2 Answers

GPA 8.3
600 Points
6 Subjects
Is each subject worth 100 points?  
If I divide 600 by 8.3, I come up with 72.2891566 (rounded to 72.3) That's a low "C" average in my book.
Generally, a Grade Point Average is calculated by assigning point value to the letter grades:
A = 4 points
B = 3 points
C = 2 points
D = 1 point
F  = 0 points

For example:  I have grades as follows:
Math = A ( 4 points)
English = A (4 points)
History = B- (3 points)
Chemistry = C+ (2 points)
Physical Education/Tennis = A (4 points)
Journalism = A- (4 points)
French = C+ (2 points)
I add up my points  4, 4, 3, 2, 4, 4, 2, for a total of 23.  
I have 7 classes.  To get the average, divide the points(23), by the number of classes (7).
My GPA is 3.28571428,  rounded to 3.3  (which is a "B" average) 

I don't understand this scoring...did you get 8.3 of 600 questions correct? 8.3% of them correct?  600 questions in each course? if not you need to break down your scores per course- beacause they will be weighted differently.