Cumulative Average on a worksheet

Can someone give me direction on what I need to do? We recently began
keeping attendance during church worship services at our church and I have
created a worksheet that we can input the info in and it will total it at the
bottom of the sheet. I have allowed for about 40 weeks of input but we are
only on week four. What I would like to do is have a formula under the cell
for total that would let me
see what our average number is in the worship services on a weekly basis.

As long as the cells for future weeks are blank, you can just use the
AVERAGE( ) function. If your attendances are to be held in the cells A1
to A40 and you have the formula =SUM(A1:A40) in A41, then put this in
A42:

=AVERAGE(A1:A40)

It will automatically adjust as you enter new attendances each week.

Hope this helps.

Pete