SUMPRODUCT based on cell values from a different column

[Frenzyy]

Hi, I've got the below SUMPRODUCT which works fine but I'd like to make it so that I don't have to specify the range for it whenever it changes. I've tried using IF of sorts but couldn't really get it to work, so thought I'd reach out.
In short, instead of specifying the range, I'd like it to just say e.g. "AA:AA", etc. and ONLY consider values for the calculation if the corresponding value in column 'A' = "XX".
Please also note that values start in row 4 and the header is in row 3, and that won't change.

=SUMPRODUCT(AA4:AA147,$N$4:$N$147)/SUM(N4:N147)

Many thanks!

[AliGW]

There are instructions at the top of the page explaining how to attach your sample workbook.