Percentage function for a group based on another group

I have two grouping levels in a report. Group A can have a Percentage() of the entire report and so can Group B, but I would like to know the Percentage() of Group A of Group B. Even if I c开发者_JAVA百科ode it, it seems like once the inner and outer groups have created their footers, I can't go back to to the inner group and set it's value.

Example:

Group A Total 50 Group A percentage of Report Total = 33% Group A Percentage of Group B Total = 33% but I want 50%

Group B Total 100 Group B Percentage of Report Total = 66%

Report Total 150

Had to handle this in the datasource. Access 2007+ now has this built in their grouping feature.