I have a spreadsheet that is assigning a number to a cell based on a
VLOOKUP. For some cells, the number doesn't exist yet, because we
haven't arrived at that moment in time yet (some cells will be
populated in the future). In those cases, the VLOOKUP'ed cell is
displaying a "#N/A". I want to average a range of the cells that have
numbers in them. For instance:

Cell K3 = 3
Cell K4 = 4
Cell K5 = 5
Cell K6 = #N/A

Obviously, I could do an "=AVERAGE(K3:K5)" and when there's data in
K6, change the formula to include K6 (=AVERAGE(K3:K6). However I
don't want to do that. I want this spreadsheet to be usable by
someone who doesn't manage formulas. I just want her to plug in the
letters, that the VLOOKUP assigns a number to, and have the average
calculate.

TIA.