pivot reports - limit report to last 20 dates

[Pivot Help]

I have three columns in my source data: date, number, text. I would like to
create a report to average all the numbers. My problem is I want to limit
the report to the last 20 days of data. How can I do this?

 

[Landxlii]

Put the "date" field in the "row" area of the pivot layout as well as in the
"data" area.
In the data area, average the date field as well as the number field.
In the row area, double click the date field to get the field options.
Click advanced and then the top 10 autoshow.
Change the top 10 to top 20.
This shows the highest 20 dates (latest).