am creating a cross tab

in that am using percentage as summarization fields and because of that my total is also becoming percentage

ex:_



Name---jan----feb------march--total

xyz------10%---20%----30%---- 25%



in total i want the average how can i do that

10+20+30 / 3 = 30 %

if i change the summarization field to avg all values change .. is there any method other method to change the formula in total