Aggregation/Summation of text and numeric fields

Question

Raw data

SiteName-----Agency------Staff Numbers

  Site1-----------A1------------10  

  Site1-----------A1------------12

  Site1-----------A1------------11

  Site1-----------A2-------------5

Wondering how I can get the following in my pivot report;

Site1-------------A1/A2---------33/5

a summation/aggregation of both the "Agency" and "Staff Numbers";

Note that I have successfully aggregated on the "Agency" field (text) using concatenatex with a "/" delimiter, but when it comes to the "Staff Numbers" field (numeric) I am not getting any summation of the staff numbers.

I get;

Site1--------A1/A2----------10/12/11/5--------> this is undesirable

I want;

Site1--------A1/A2----------33/5---------------> this is desirable