Hello,

I am trying to come up with a formula that will help in calculating
averages in my visitor tracking spreadsheet. My spreadsheet has a lot
of visitor demographics and head count data entered by day. Across the
top, I have dates as column labels. Down the side, I have different
visitor demographic age ranges as row labels. On the lowest row, I
have a total of all the visitors in any given day.

Other info: We are only open Monday - Saturday, so I only have those
dates across the top. Also, below each day there are two sub-columns-
Male and Female.

I need to add up all the visitor totals for each day so I can get an
average number of visitors on Mondays, Wednesdays, Saturdays, etc.

I have tried to modify this formula which I've used to count the
totals in every other column:
=SUMPRODUCT(--(MOD(COLUMN(5:5),2)=0),5:5)

But it does not work because it only counts every *other* column, and
what I need to do is count every 12th column.

Can anyone help?