Suppose I have a column of numerical data, say, in Column A.

I want to compute average, e.g., average(A1:A1000).
But sometimes I want to compute average(A23:A1000) or
average(A48:A1000).

Is it possible for me to input the bottom of the range, say "A36", in
another cell, such as C1, and then compute
average(whatever cell is specified in cell C1,A1000)?

How do I do this simply?
MD