How does Dota 2 Spell Damage calculation work?

Question

What I believe it is:

Magic Resistance = 1 - (1 - [Hero Base Magic Resistance]) * (1 - [Strength * 0.0008]) * (1 - [Any Magic Reduction Item/Ability 1]) * (1 - [Any Magic Reduction Item/Ability 2]) ... * (1 - [Any Magic Reduction Item/Ability 1 N]) * (1 + [Magic Increasing Item/Ability 1]) * (1 + [Magic Increasing Item/Ability 2]) ... * (1 + [Magic Increasing Item/Ability N])

Spell Amplification = (1 + [Intelligence * 0.0007] + [Magic Increasing Item/Ability 1] + [Magic Increasing Item/Ability 2] ... + [Magic Increasing Item/Ability N])

Damage taken in HP = Spell Damage * Spell Amplification * (1 - Magic Resistance)

Answer 1

That is correct. The way i think about it is that multiple factors of amplify/resist spell damage add, not multiply.

So if let's say you have 3 factors that amplify the dmg, you actually do (initialDmg + 50% + 50% + 50% = 250%), not (initialDmg + 50% + 75% + 112.5% = 337.5%). This could lead to huge amounts of dmg.