I would create another column somewhere to the side that multiplies the year
times the number of members born that year (i.e. =1918*4) to get a total
number (1918*4=7672). Total that column and divide by the number of members.
You can hide that new column once you've finished the formulas.

There might be an easier way, but that's the best way I know how to do it.

Hope this helps.

"Roger" wrote:

I created a spreadsheet with 2 different fields.
Birth Year Mbrs
1918 4
1919 5
1920 4
1921 6
1922 11
As we have 4 members born in 1918 and 5 mbrs in 1919 etc.
Thank you
--
Roger