[Orgmode] evaluating rows or columns in org-table

[Kene Meniru]

  |   |   | names      | grade 1 | grade 2 | grade 3 | Total |   | 
Letter grade |

|---+---+------------+---------+---------+---------+-------+---+--------------|
  | # | 1 | student 01 |   91.80 |   96.40 |   97.00 | 95.07 | 1 | C 
         |
  | # | 2 | student 02 |   88.78 |   89.15 |   98.00 | 91.98 | 2 | B 
         |
  | # | 3 | student 03 |   92.00 |   95.14 |   97.00 | 94.71 | 3 | B 
         |
  | # | 4 | student 04 |   84.00 |   74.62 |   88.00 | 82.21 | 4 | B 
         |
#+TBLFM: $7=($4+$5+$6)/3;%.2f

Sample letter grade calculation:
90-100 = A
80-89  = B
70-79  = C
60-69  = D
 0-59  = F

I am deeply sorry if this has been addressed before here. I have 
searched but could not find any reference.
I am a teacher and have been using org-mode in combination with noweb as 
a class manager. I also use moodle and blackboard but I like to keep my 
lecture notes and student grades local on my machine. I typically have 
the above table for student grades (usually substantially more than 
that). I am able to calculate many things like averages, etc., but would 
like to have letter grades and "best performing" comments by the 
students doing as well.

Starting with letter grades, is there a way I can evaluate the Total 
column and assign letter grades as shown above? Thanks


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Kene Meniru
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