Why are you subtracting 10 from the armor reduction? The character has no armor penetration, not to mention even if it did that is not how it would be calculated.
Nor is this how 10% bonus from Weapon Mastery is calculated either, it is multiplied into the final damage, not subtracted from damage reduction granted by armor.
Same goes for the plus 50, and additionally since the two talents are not the same type (ie: Weapon Mastery is affecting all melee damage, while Elemental Weapons only affects weapon enchants, they should not be added together but rather multiplied).
I advise looking for archived elitistjerks and old wowwiki articles if you are unfamiliar with how these formulas work.
http://wowwiki.wikia.com/wiki/Damage_reduction - determining damage mitigated by armor
http://wowwiki.wikia.com/wiki/Sinister_Strike_formulas - a general example of how damage multipliers are handled

