Accessing the field values in different fields for calculation

Hi,

I am creating a report in which I have used breaks for grouping the customers by their category. I have used summary on the amount field to calculate the sum in the individual category and also for total amount.

Now, I also want to add an column which could display the percentages of individual contributions.

So, its like I have to write a query accessing the total percentage, categorized percentage and individual amount.

My question: How can I access the various fields values in the query of some other field specifically sum and total sum( because it shows the sum([Amount]) for category sum and total sum both)

-BOBJuser