calculate on days between min and max date in group

[MarLone]

Hi,

Is it possible in QS to calculate on days between min and max date in group?
If I have two different date fields (date_start and date_completed), And when I group them I get i.e three different dates in each group. Then I do summarize to see the minimum date of first group/field and maximum date of second.
And when I try to calculate the days between those two I got the following error massage:

“One or more of the report items that you selected does not support this action. Select different report items or a different action.”

I can do the no of days calculation on all other dates between those two fields except on summarized (min and max).

Is there any workaround on this?
Thanx