Thanks a lot for your help. The formula you provided worked OK. I have QV Personal Edition, so I can't open other's files.
Regarding to showing the same by week, I would like to know how can I create a pivot table, using "Week" as a Dimension, but showing the last 3 weeks (I think I have to edit the dimension). I.e.: I have the following weeks: August01 - August08 - August15 - August22 - August29 - September05. I want to show only data for last 3 weeks, but not filtering the last 3 weeks, I want all data avaiable.