Average of Distinct values

Hello, 

Below is a snapshot of my table structure. In my graph i am dispaying the weekly sum allocation for each project and in the other graph I am showing total allocation for each resource in month/week ( I have attached two graph snapshot in my question).

Table Snapshot

Now , I am trying to show the  total average allocation percentage of a resource (all projects) in a selected date range. 

If you see my graph in the questions, In september total allocation is 85 and in Oct & Nov, total allocation is 80, And in december it is 35. I need a score card which shows the average allocation of resource in 4 months. (85+80+80+35)/4

Please let me know if this helps. 

Thanks