28 10 | 100
29 210
30
40 20 | 84
41 130
42
43 30 | 75
44 740
45
46 40 | 73
47 220
How can I sum every 3 rows A29+A41+A44+A47+... I tried various suggestions like this and this one but couldn't figured it out.
In addition, is there any way to extract the second part, to a different column, of the other rows? I mean 100, 84, 75, 73, ...
In a cell as a standard non-array formula,
=SUM(INDEX(A29:A48*NOT(MOD(ROW($29:$48)-29, 3)), , ))
The ROW($29:$48)-29 is the position within A29:A38 and must be expanded if A29:A48 is expanded.
来源：https://stackoverflow.com/questions/35664572/sum-every-nth-rows-in-excel