random number sum macro /formula

[aiims]

Hi All,

I am trying to do a simple calculation but not able to find the right way.

level 1 level2 level3 level4 level5 level6 Sum
1 1 2 3 20 6
1 3 3 3 6 7
1 3 3 3 1 1
5 9 14 3 24 25
6 10 15 20 25 25
7 11 16 21 26 25
8 12 17 22 27 25
9 13 18 23 28 25
10 14 19 24 29 25

i have these 6 levels, All i want is the sum or sumproduct of last three columns - (Now 3 is user specified , a user can put any number between 1-6 and i should get the sum of those count).

For example :If the user input is 3 the I should get a sum of level 6 ,level 5 and level 4 as those are the last three in the list
File is been attached .

NOTE:- Its possible we might get more than 6 levels sometime.
Please help me with macros or formula to sort this.
I tried offset condition but its giving the wrong results.

Many Thanks
Sam

[daddylonglegs]

Try this formula in G6 copied down

=SUM(OFFSET(F6,0,1-O$2,1,O$2))

[aiims]

Thank you so much for the reply daddylonglegs ,
It was really a great help for moving forward however i am stuck with another situation here,

Sumproduct - ii not able to get this .
I am really new to excel and trying to bring my life into this,please help

attached is the sample file.
Many Thanks
Sam