Percentual damage reduction?

[quote=caspercom]Ok, so we have all kinds of abilities/items/masteries etcetera that reduce incoming damage by a set percentage. My question is: how do these stack? Example: [list] I'm playing Galio and I use my ult, reducing incoming damage by 30%. My defensive mastery tree is built up to the highest rank, giving me 4% reduced damage. Because my killstealing skills are awesome, my leviathan has 20 stacks, reducing damage by 15%. Our ever friendly allied Maokai uses his ult around me, adding 20% damage reduction. [/list] Does this mean I have 69% damage reduction or do they stack differently? And if they do, in what order?[/quote]

[quote=Lugignaf]I think they stack multiplicatively. So you would get about 57% reduction if my math is right and they do indeed stack how I think they do.[/quote]

[quote=Nighthawk]Nah. As far as I know they stack additively. Essentially if you have 100% reduction, you take no damage. However it could be that i'm thinking of percent armor reduction or something...[/quote]

[quote=Searz]They stack multiplicatively. 54.3%reduction.[/quote]

[quote=Temzilla]It's .7 (100%-30%), .96 (100%-4%), .85 (100%-15%), .8 (100%-20%) So, .7*.96*.85*.8 = .45696 So you would have 54.304% damage reduction. Basically, this would apply after armor/MR. With your base of 85 Armor, you would have 79% Damage reduction against physical attacks.[/quote]