增删行都能自动求和 (12511)

A3:A5=IF(C3="","",MAX(A$2:A2)+1)

A3複製到 A7  A11 後下拉

C3{=SUM(OFFSET(C3,,,MATCH(1=1,ISERR(-A3:A12),)-1))

C3複製到 C6  C10 後下拉

C13=SUMIF(B2:B12,"",C2:C12)

另解C13=SUM(C2:C12)/2