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# Thread: Summing every third cell in a range

1. Is it possible to sum every third cell in a column?
- where the number of entries is variable, and
- ignoring cells with text in them

2. Yes

Are you familiar with macros???

3. If A2:A11 contains...

{10;20;30;4;5;"dog";12;11;7;6}

...the array formula...

{=SUM(IF(MOD(ROW(A2:A11)-ROW(A2)+1,3),,A2:A11))}

...produces the value 37.

Note: Array formulas must be entered using the Control+Shift+Enter key combination. For more on array formulas see the Excel Help topic for "About array formulas and how to enter them".

4. An array formula to sum every 3rd.
Enter it with Ctrl-Shift-Enter.

For ease of use:

The first amount to be summed should be in a row that is divisible by the Nth factor.
Example Row 9/3

One can insert or delete row to accommodate this.

=SUM(IF(MOD(ROW(A1:A17),3)=0,A1:A17))

or more generic
Nth 3 or alternative
rD range of numbers
=IF(Nth=0,0,SUM(IF(MOD(ROW(rD),Nth)=0,rD,0)))

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