Help with creating an Average measure for three columns

Hi Everyone
I was wondering if someone can please help me with the following problem.
I have a power pivot table which consists of the following:
Dept Name, Score 1 Rank, Score 2 Rank and Score 3 Rank
The ranks are all measure calculations.
Dept Name Score1 Rank Score 2 Rank Score 3 Rank
A n/a 2 1
B n/a n/a 2
C 1 3 3
What I need is to create a measure which calculates the average of the three ranks
i.e. Dept A = overall rank = average (score rank 1 , score rank2, score rank3)
I try to use average a or average x but it say I can only use one argument and not all three.
I also need to ignore the blanks so the average function is most suitable rather than adding and dividing by 3.

Is the a way to do this.

Thanks in advance

Thaks for the reply

I have tried Calculate but am getting no luck with average function in calculate because it only lets me choose two columns and bot three

Can you post a sample workbook so we can see the actual data set up?

Dear noboffinme

Thanks you for replying. I need to mention that I am using Power Pivot and not normal pivot and when I create a measure with Average(a1,a2,a3) for example I get the following
Too many arguments were passed to the AVERAGE function. The maximum argument count for the function is 1.
a1,a2 and a3 are measures which are reated from three different tables but all have a relation with each other with a common field.