One of the analyst's in my office found an interesting bug/quirk in the Interactive reports of APEX 4.2...
So basically if you select the function in the first row of Sum as you can see none of the other functions selected after that display.
Count Distinct Count Median Minimum Maximum Average Sum
Sum No No No No No No No
Average No No No No No Yes
Maximum No No No No Yes Yes
Minimum No No No Yes Yes Yes
Median No No Yes Yes Yes Yes
Count No Yes Yes Yes Yes Yes
Count Distinct Yes Yes Yes Yes Yes Yes
Would be interesting to see if this is a feature or bug/quirk that can be repaired in the next release..