Create Running total for selected groups

Hi,

I was hoping someone could help me.

I am new to Webi (8 weeks in!) and I am using WEBI 4.0 .

I have created a report which is grouped by the dimension Group [Group 1, Group 2, Group 3 etc]. I have set this to be a section on my report and I have created some totals by these groups. However I now need to create some summaries of these groups. For example add groups 1,2,3,4 together, then 5,6,7 then 5,6,8 etc.

I an sorry if this sounds simple but I just cant see to work out how to do it.

Many thanks and again apologies for my lack of knowledge.