How does 50% extra xp weekend stack with other bonuses?

Question

Blizzard is doing a +50% xp weekend in Diablo 3, and I'm wondering if and how it stacks with the other xp bonus' from difficulty tiers.

On Expert

• Additive:
  • (1+difficulty+.5)*base
  • 1k xp monster in normal now equals 2.5k xp
  • Net gain = +150%
• Multiplicitive:
  • (base + .5*base)*(1+difficulty)
  • 1k xp monster in normal -> 1.5k xp with weekend bonus -> 3k xp on Expert
  • Net gain = +200%

the quantifiable difference really becomes apparent at higher difficulties:

On Torment IV

• Additive:
  • (1+difficulty+.5)*base
  • 1k xp monster in normal now equals 9.5k xp
  • Net gain = +850%
• Multiplicitive:
  • (base + .5*base)*(1+difficulty)
  • 1k xp monster in normal -> 1.5k xp with weekend bonus -> 13k xp on Expert
  • Net gain = +1200%

As players it is definitely to our advantage if they are using multiplicitive bonus instead of additive. Does anyone know which Blizzard is using?

Answer 1

These are the numbers taken from the game interface with

Community event Buff - Your experience gain is increased with 50%

On N  0%    bonus ->   50%   Bonus Experience
On H  75%   bonus ->  162,5% Bonus Experience
On E  100%  bonus ->  200%   Bonus Experience
On M  200%  bonus ->  350%   Bonus Experience
On T1 300%  bonus ->  500%   Bonus Experience
On T2 400%  bonus ->  650%   Bonus Experience
On T3 550%  bonus ->  875%   Bonus Experience
On T4 800%  bonus -> 1250%   Bonus Experience
On T5 1150% bonus -> 1775%   Bonus Experience
On T6 1600% bonus -> 2450%   Bonus Experience

So on Normal: 1000 Exp becomes 1500 instead of 1000 (50% total increase)
So on Hard  : 1000 Exp becomes 2625 instead of 1750 (50% total increase)

Im not gonna do that math for the rest but I assume they are either perfectly correct or close within a rounding error of being correct.

Answer 2

In the past, it has been additive, but you should be able to check out your character sheet (inventory->details) and it will have a bonus XP percentage stat on it.