So you actually want the average?

One way:

=AVERAGE(OFFSET(A1,99,,-B1))

--
Biff
Microsoft Excel MVP


"Eric" wrote in message
...
Does anyone have any suggestions on how to use Indirect function?
For Example, there is a list of numbers under column A, a given number 20
in
cell B1 and a formula sum(A81:A100)/20 in cell C1.
If I change the number 20 into 30 in cell B1, then the formula will become
sum(A71:A100)/30.
If I change the number 20 into 40 in cell B1, then the formula will become
sum(A61:A100)/40.
Does anyone have any suggestions?
Thanks in advance for any suggestions
Eric