I would think it best to use a helper row, if possible Need to get one of
these rows to invert.

If you can do this, and yoru Row 3 is always 1 - x in order, go to, say, row
5 and enter

=MAX(3:3)-COLUMN()+1

in the first cell and copy to the right as much as needed, then it's a simple

=sumproduct(A1:D1*A5:D5)

"BorisS" wrote:

I need to sum (entered as array in one cell) a series of cells that go up
multiplied against a series of cells that go down.

I have a row of four cells
A B C D
Row 1 2 5 3 6

and another row
A B C D
Row 3 1 2 3 4

the formula I need (my attempt at which is:
=SUM(A1:D1*OFFSET(G28,0,-1*A3:D3+1))

should do the following:
multiply A1*D3
multiply B1*C3
multiply C1*B3
multiply D1*A3

and sum them up.

Where am I going wrong?
--
Boris