Let E= Exam1 + Exam2 
(HW grades are not included since data from all 4 homeworks
are needed to make sense of their contribution.)

  < E <    Letter Grade
390 -  501    A
270 -  390    B or B+
220 -  270    C or C+
 0  -  220    F

The class average for E is 299.333 (over the 27 students participating
in Exam 2.)