Calculation Help Report

Content

Name	Weight	Numeric Rating * Weight / 100
Competencies	15.	0.45
	17.	0.51
Goals	20.	0.6
	25.	0.75
	30.	0.9

I have a report that spits out like this.  The last column is Rating * Weight / 100.

What i now need to do is add a new column:

Sum of "Weight Numeric Rating * Weight /100" / Sum of weights / 100 by first column (Goals or Competencies).

Any idea how i can add that in?  

Thank you.