Damage reduction Question

Before i go through the small troubles of testing this. Does anyone know how damage reduction works.

For say... i have 100 life, and 0 armor. An enemy does 20 damage. It attacks me, i have 80 life. But if i have a 5 damage reduction, i will have 85 life.

Lets say i have 100 life, and 1 armor(6% reduce). The same enemy attacks me, dealing 18.8 damage to me. Does the 5 damage reduction occur after armor, or before. the difference is this. (after armor) he deals 13.8, Before the armor, 14.1 Thats a small difference, but in enfos, like when enemies are dealing 5000 damage, its alot. Also, does it stack?
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Say i have 2 -5 damage things, he would deal 10 damage to me, or just 15 because they dont stack?

I would say:

You have 100 hits, 10 reduction and 1 Armor:
You get hit for 100 dmg... first there comes the armor ... = 6% => 94 Dmg.. dann 10 reduction is 84 damage.


But why dont you just TEST it?