Can you create a calculated column in a Summary Report that uses other columns in the report to generate the final column?

Does just making one of the columns on the report a formula field and doing the calculations in there not work for this? I thought using a calculated column to add up other columns on the reports worked too, I am almost positive I have summary reports like that.

It's possible I am missing something obvious here though. It sounds like you want something pretty simple, a column that will divide column 1 by column 2 and have the result in the 3rd column. Is that right?