=(SUM((IF(MOD(ROW(A1:A40),$F$4)=0,1,0)*(A1:A40))) )/(SUM((IF(MOD(ROW(A1:A40),$F$4)=0,1,0)*1)))

You can reduce that to:

Array entered.

=AVERAGE(IF(MOD(ROW(A1:A40),F4)=0,A1:A40))

--
Biff
Microsoft Excel MVP


"dhstein" wrote in message
...
If F4 contains the value "12" then you can use this Array formula:

=(SUM((IF(MOD(ROW(A1:A40),$F$4)=0,1,0)*(A1:A40))))/(SUM((IF(MOD(ROW(A1:A40),$F$4)=0,1,0)*1)))


Array formulas are entered by typing the formula and instead of hitting
"Enter" key - hit "CTRL + SHIFT + ENTER" simultaneously. You can learn
about
array formulas he

http://www.cpearson.com/excel/ArrayFormulas.aspx



"uiowa" wrote:

Hi,

I am struggling to figure out how to take average of every twelfth cell
in a
column containing a very
list of numbers.

Can anyone help me?