hmm...tried to reply but didn't happen...hope i don't reply twice by mistake
Can you attach the sheet? I would guess that your result I4/F4 is evaluating to something close to a value and "appears" to be equal to one of those values based on the number of decimal points you are showing. The way you have written the formula would produce a "FALSE" if that value (I4/F4) didn't EXACTLY equal one of the values from A4 to A8 (your last IF statement has no instruction for the FALSE case).
For instance if,I4 = 9 and F4 =2.99, then I4/F4 would look like 3 or 3.0 but would not be "equal to" 3 or 3.0.
But, w/o seeing the sheet, not sure what you are trying to do exactly. Are you trying to set up a range of values to produce a grade? Like A3 = 100, A4 = 90, ... B3="A", B4="B"??