March 25, 2003.
Let your Exam1 grade be E1 (max is 100).
Let your Exam2 grade be E2 (max is 350).
Let E = E1 + E2.

If  375 <= E <= 450    MidtermPerformance is about A
If  350 <= E <= 375    MidtermPerformance is about B+
If  300 <= E <= 350    MidtermPerformance is about B
If  250 <= E <= 300    MidtermPerformance is about C+
If  220 <= E <= 250    MidtermPerformance is about C
If  200 <= E <= 220    MidtermPerformance is about D
If    0 <= E <= 200    MidtermPerformance is about F

Note 1. Boundaries are fuzzy. For example a 375 may be an A now,
        but in the final a proportional grade may be a B+.

Statistics:
  Ex1+Ex2 : Average is  327 and median is 339
  Ex2     : Average is  262 and median is 275