Group two fields as one and show their sum

Group two fields as one and show their sum

I have a list, which has.
PropName PropCount
IA 20
IB 40
ID 10
IC 20
All i wanna do is now to group them as.
PropName PropCount
IA/IB 60
ID/IC 30
and thus show the count of both of them in one as this is the requirement
i need to fulfill.
Help !.