I am trying to figure out a formula for excel to look at two columns and
average the data in one of them if a certain number is in column A.

Example: I want Excel to look at the contents in column A for a range of
cells and if the content is the number 1, I want it to then average the
contents of what is in column D for all rows that have a 1 in column A.

I have tried using IF and average and I just get a return of #value. I
tried =average(if(a1:a20="1",d1:d20)) but it returns the error even when I
enter it as an array formula.

Any help is appreciated.