Question About Physical Resistance

[Pansesus]

Something is bothering me a lot these days. I created a summoner Necro and he has passed hell act2. It could be certain that both AD and Dec could pierce bosses's physical immue with Physical Immue + Stone Skin attributes, but what is the final Physical Resistance after these two curses have applied on those tough guys, 80% / 90% or 70% / 60% or even some other percentages? I am just a little bit confused.

Cheers