Post-BB paladin dual charge and dual weakness

I believe single charge will be full elemental, but dual charge will be half elemental. I'm not sure if it's additive or multiplicative though. I'm assuming additive.

On neutral mob: (holy + lightning)
(1 + 0.25 + 0.35) x 1 = 1.6x
On holy or lightning weak, not both:
(1 + 0.25 + 0.35) x (1 + 0.25) = 2x
On holy weak, lightning resist (yeah, doesn't exist):
(1 + 0.25 + 0.35) x (1 + 0.25 - 0.25) = 1.6x

On neutral mob: (just holy)
(1 + 0.35) x 1 = 1.35x
On holy weak:
(1 + 0.35) x (1 + 0.5) = 2.025x

Are the % of the charges added? I really thought multiplied... =O