On 2002-09-26 20:56, Carl B wrote:
C10:C67
=SUMPRODUCT((MOD(ROW(C10:C67)-CELL("Row",$C10)+H1,H2)=0)*(C10:C67))
where H1 houses the index that indicates the value to start with from the set of values of interest and H2 the index that indicates the
Nth value to sum.
If you want to sum beginning with the first value, set H1 to 0. Since you want to sum every 3rd value, set H2 to 3.
Tom Urtis/Juan Pablo: This formula in fact reduces 4 different formulas to just one with 2 parameters (see Pearson's SUMEVERY.XLS). It's independent of the native row/column number. I remember attempting such a formula at the old board in an exchange with Juan but failed to succeed. I had promised myself to dedicate such a formula to Juan if I could build it.
Aladin