We are calculating resource productivity and I have attached the screenshot for your reference.

I was able to calculate productivity session wise as well as date wise(per day) but resource wise:

Productivity session wise = Total Author duration/available duration in office for that session(pre lunch)= (2/3.5)*100 = 57.14%(row 4, column F in screenshot)(used formula field in object to calculate this)--- I was able to do this

Productivity date wise(per day) = average Total Author duration per day/Sum of available duration in office = 3/(3.5+4.5+0.5+0)=23.53%(row 3, column H in screenshot)(used formula functions on the report)--)--- I was able to do this

I got stuck while calculating Below values:
Productivity per resource =average of Productivity date wise(per day) =23.53(for date 5/15/2015)+33.33(for date 5/16/2015)+8.33(for date 5/17/2015)/3(number of days)=21.75%

or
if the below is pssible, it would be fine

Productivity per resource = sum of average Total Author Duration per day/Sum of available duration in office=2( (Author average duration for date 5/15/2015)+ 4(Author average duration for date 5/16/2015) + 1(Author average duration for date 5/17/2015)/=3.5+4.5+0.5+0.0+4.0+6.0+0.5+1.5+4.0+6.0+0.5+1.5(column E)=21.53%

Since I have used formula functions on the sanpshot report for calculating Productivity date wise(per day), I'm not able to re use or reference them in other formula functions

The source report I'm using is a tabular, since I want the sessions on snapshot I could not use summary report as a source

Your help is much appreciated:
sorry for the lengthy explanation :)