Average Percent in sub report

[goodkarma]

I have a Crystal report version 6. The report has a subreport and in the subreport I'm getting a production efficiency based on total hours paid(in subreport) verses total hours worked(in main report) I'm passing the total hours worked in as a parameter field and am using a formula to get the efficiency. This efficiency is broken down into groups(areas). I am now trying to add up all the individual efficiency percentages for each area and get an overall efficiency percentage for the given Business Unit. For example this is one groups efficiency.
Total Hours: 1,269.25
DL Efficiency: 88.97%
So say I have 20 different areas how can I get the overall efficiency? Any help would be GREATLY appreciated!!!