Add the grades of Exam 1 (0-140pts) and Exam 2(0-333pts) and the two homeworks (20 pts each)
Let G= Exam1 + Exam 2 + HW1 + HW2  (0 - 513)
 
 A    range : 435 - 513
 B/B+ range : 370 - 435
 C/C+ range : 240 - 370
 F    range :  0  - 240

[Boundaries possibly overlapping]