how to get partial results from total in pivot table

Hi there,

I have a daily file that I update where I have all the receipts approved. All those receipts have different categories, and we need to review, on a daily basis, the 30% of the total volume for check purposes. I have a pivot table there, and I would need to have automatically the 30% of the total volume (even random) to review, so my analysts can go there an easily check this volume. How can I do that in excel?

Your help would be very much appreciated. Thanks in advance.