Does anyone know how to create an array that multiplies 2 numbers together
but selecting the first number in one array multiplied by the last in the
other array. Then the second number multiplied by the second last?

Eg
I have two arrays that I want to show in rows across my workbook (not
columns down the page):
Array A 3,1,2,1,2
Array B 10,20,30,12,15

I wish to perform the following calculation:

3 x 15 + 1x12 + 2 x 30 + 1 x 20 + 2 x 10
ie working from left to right on Array A and Right to Left on array B. This
is simplified calculation and I would like to run this for over 100 numbers
in each array.

Sumproduct doesn't do the right calculation as it works from left to right
on both arrays. I have seen an add-in used to so a "suminverseproduct" or
"sumreverseproduct" but do not have access to this anymore.

Does anyone know how to do this calculation or have an addin (xla file) that
will do this?

Thanks

Alastair