Figuring letter grades

I have a worksheet, that has about 25 students on it (rows 1-25) There are 25 assignments (25 columns) Each assignment has a points possible that sums to the end, total points possible 1,000. I post each students assignment grade, and it also sums to the end. My question, what would be the best formula for looking at the students total points, and figuring their grade, Based on this scale. I could do it by hand, but I know there's got to be a formula that will calculate and post a letter grade, based on the calculation.

900 –1000 points = A
800-890 points = B
700–790 points = C
600-690 points = D
0 –590 points = F

As always any help is appreciated.

In a table, have two columns, the left one with 0,600,700,800,900 and the other with F,D,C,B,A. Then, if this table is in G1:H5 and the student's total score is in E2, F2 could be =VLOOKUP(E2,G$1:H$5,2,True) and that could be dragged down.