Copying a formula horizontally, skipping 2 colums each time.

[jumbles]

Hi,

I'm trying to sum every third column in a portion of a spreadsheet, and copy the formula horizontally.

For example,

Cell A1 = Sum(M:M)
Cell B1 = Sum(P:P)
Cell C1 = Sum(S:S)

Thanks

[Marcol]

Try this

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This is volatile so best to restrict the base column to a known range
e.g.

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[EDIT]
This non-volatile formula is probably better

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[jumbles]

Thanks! The third one is working well for me. What does the COLUMN(A$1) part do?

[Marcol]

COLUMN(A$1) returns the column number for cell A$1 i.e. one.
We multiply this by three, so when dragged right we get 3, 6, 9. 12, etc.
The syntax for INDEX() is
INDEX(range, row number,column number)
So we get the 3rd, 6th, 9th. 12th, etc. column from range $K:$Z. (By leaving row number empty we get all the rows in the column called.)

[jumbles]

Thank you!