Am i working out the AAR correctly?

Ghostboytjie

Now Biohazard Has a 20% chance to bleed per hit.
Blade Reduces Ability Accuracy by 40% and Parry Reduces Ability Triggers by 30%
For me that means there is a 70% ability Reduce if i parry and hit while opponent are stunned.

70% of 20% is 12 so does that mean that Biohazard only has a 8% chance to Trigger when i parry and hit while opponent is stunned ? or a other presentage?

DNA3000

Now Biohazard Has a 20% chance to bleed per hit.
Blade Reduces Ability Accuracy by 40% and Parry Reduces Ability Triggers by 30%
For me that means there is a 70% ability Reduce if i parry and hit while opponent are stunned.

70% of 20% is 12 so does that mean that Biohazard only has a 8% chance to Trigger when i parry and hit while opponent is stunned ? or a other presentage?

The mastery you're referring to is Pacify, not Parry. Pacify grants a reduction of ability accuracy depending on rank (30% at max rank 3). I believe the way you are interpreting the mechanics is correct, although this is something I haven't explicitly tested myself. Most independent percentage modifiers that are not flat stats stack linearly with each other before being applied to the base value of whatever they are modifying (although there are exceptions: there always are).

(Actually, I believe all modifiers act independently on the base value of the thing being modified, but mathematically that's the same thing for linear modifiers, and it's easier to say the percentages add together).