yogi_Set Up Formula For Computing Sum of Last Specified Number Of Columns Of A Table -- Solution 2

                                          Google Spreadsheet   Post  #1098
Yogi Anand, D.Eng, P.E.      ANAND Enterprises LLC -- Rochester Hills MI     www.energyefficientbuild.com.    Apr 7, 2013
user Jimmy Lucich :(http://productforums.google.com/forum/?zx=imdn03xd4ulc#!category-topic/docs/spreadsheets/7cBBo4DKGhA)
I'm trying to figure out how to add a column that only adds the last 10 (or whatever # I decide) columns on a sheet. 

So I would then have both my total of all columns and then this new "running average" of the last 10 columns only. Then, as I add data to empty columns, or as I add columns, only the 10 most recent (columns) of data are used and the 11th 'most recent' column would be dropped and not counted. As an example:

Suppose Columns A -- T. This "New column" would add only columns K--T. then, once column U is populated, this "New column" would add columns L--U, etc. 

Any formula, lookup that would do this would be most appreciated. Thanks for any help!

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following is a solution to the problem with SUMS and AVERAGE computed to the right of the table. In my opinion, the solution provided in my last blog post:
http://yogi--anand-consulting.blogspot.com/2013/04/yogiset-up-formula-for-computing-sum-of.html
provided for a more generalized solution where any number of entries could be made to the right
in any event ... here we go