calculating percentages in cross tab

Hello,

           I have a  report with a cross tab summary in the report footer.

My cross tab looks like this

                               column 1          Dept 1                          dept 2

                        column 2          total patients   13         total patients      15   

Practical problems                 @ count of patients = 1       @ count of patients = 5

Treatment decisions               @ count of patients = 2     @ count of patients   = 4

                                                                                                                               dept 1                          dept 2

I want to display percentage of patients for each problem eg: practical problem %= 7.69% ( 1/13*100)          33.33% (5/15*100)

Can someone help me with this?

Thank you

Sandhya