Hi!

Assume you want to sum cells A1, D1, G1 and J1.

Since that's not a very big range I would just use:

=SUM(A1,D1,G1,J1)

If you have a larger range, every 3rd cell from A1 to BA1:

=SUMPRODUCT(--(MOD(COLUMN(A1:BA1),3)=1),A1:BA1)

Biff

"Liliana" wrote in message
...
I have a list of products on columns with the materials correspondence (on
rows). At each product I have more 2 columns that shows me how many of
each
material I need for producing a number of products. The same material is
used
by another product, so I need to sum the material needs only for the
"Total"
named columns of each product. This means I have to sum every third
column's
cell by row.
Can anyone give me some help?