This formula will sum every other row A2, A4, A6, A8, A10:

=SUMPRODUCT(--(MOD(ROW(A2:A10)-ROW(A2),2)=0),A2:A10)

This formula will sum every other row A3, A5, A7, A9:

=SUMPRODUCT(--(MOD(ROW(A2:A10)-ROW(A2),2)=1),A2:A10)

--
Biff
Microsoft Excel MVP


"Lissa" wrote in message
...
How do I write a formula to add the alternating cells in a column? It is
a
rather large spreadsheet, so entering each cell individually would be
rather
cumbersome and won't fit. Any insight would be greatly appreciated.