A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
You can use a formula like this to sum every other row:
Odd rows:
=SUMPRODUCT((A1:A100)*(MOD(ROW(A1:A100),2)<>0))
Even rows:
=SUMPRODUCT((A1:A100)*(MOD(ROW(A1:A100),2)=0))