Is the evade mastery bonus to evasion, a flat addition to your evade chance, or is it a multiplier of it?

In other words, if I have a base chance of 10%, to evade an attack, and evade mastery gives me +21% bonus, would I have a 31% chance to evade, or a 12% chance (10% x 21%). I'd assume the former, because otherwise it would be pretty worthless, but I just wanted to make sure.

Also, does evade mastery armor penalty, factor in before or after Armored Evasion?