pivot table % of

[ericlch16]

I have a pivot like that
xxx yyy grandtotal
a 10 30 40
b 5 50 55
sum 15 80 95

I want this to be like that?

I have a pivot to have another row for sum such that

xxx yyy grandtotal
a 10 30 40
b 5 50 55
sum 15 80 95
% of div 15.8% 84.2% 100.0%

is that possible? if yes, how?