Stacking Damage Modifiers

How are damage modifiers calculated when stacked?

For example:

Axes provide 20% damage bonus with GM lumberjack
Slayers do double damage (according to stratics).
Berserker talisman provides ~5% per level (+50% @ level 10).

How are these bonuses applied when there are more than one?

Multiplicative?
(base damage)*(150% Talisman)*( 120% LJ)*(200% slayer)=(1*1.5*1.2*2)=360%

Additive?
(base damage)+(50% Talisman bonus)+(20% LJ Bonus)+(200% Slayer bonus)=(1+0.5+0.2+2)=370% damage

A combination?
Example 1: [(Base damage)+(50% Talisman bonus)+(20% LJ Bonus)]*(200% Slayer bonus)=[(1+0.5+0.2)*2]=340% damage

As you can see each scenario is quite different. I'd assume that it'd a "combination" method, in which case there are MANY possibilities to plug in the numbers and operators.

P.S. My calculation were merely to illustrate the different results. I thought i should say this before the math nerds crucify me for my errors (i'm sure they're there). Those same math nerds undoubtedly know that the content of this post is still valid - depending on how you perform the order of operations, you'll get different results.

@eppy @Adam @Shane Care to reveal the code?
 
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