Calculating Average based on 3 filled cells from left in a row

[Narnimar]

I have A1 to L1 total 12 cells reserved to enter the monthly values. m1 will
have last 3 months =Average(a1:c1). I need avoid the shifting of reference
cells every month in the formula to calculate last 3 month Average. Any
alternative formula I can apply to auto calculate the Average amount based on
3 value filled cells from the left end of the row? I mean if I fill apr value
in D1, then same result from =Average (b1: d1) which should automatically
return in m1.
Thanks

 

[Gary''s Student]

To average the last three values in row #1 use:

=AVERAGE(IV1:INDEX(1:1,LARGE(IF(1:1<>"",COLUMN(1:1)),3)))

This is an array formula that must be entered with CNTRL-SHFT-ENTER rather
than just the ENTER key.

 

[Narnimar]

So I put a1 to e1 with 25 28 32 14 15 and placed this formula in m1. Its
returns 0. Any reason?

 

[Gary''s Student]

My problem... We need a small change because M1 is in the same row as the
data we are trying to average:

=AVERAGE(L1:INDEX(A1:L1,LARGE(IF(A1:L1<>"",COLUMN(A1:L1)),3)))

CNTRL-SHFT-ENTER still applies!!

 

[Narnimar]

Similarly how can I do the same if those values are in merged cells?

 

[Gary''s Student]

I have not been able to get this type of formula to work on merged cells.

 

[Narnimar]

I have one limelight in this isue! I have identically made 12 cells by merger
of 2 cells for each one. Now is it possible for a solution.
Secondly, is it possible for the right formula to get the Average value
where in jan and feb month there will not be 3 cells filled?