Point of Clarification about Phase Changes

[CollectiveRocker]

When a problem states that 3 combined substances are at thermal equilibrium at atmospheric temperature, and then we add in another substance; how do we determine the temperature of thermal equilibrium? Do I even need it?

[BLaH!]

Well if the 4th substance is at the same temperature as the other 3 then the 4 substance mixture is already at thermal equilibrium. I guess I would need to know more about the problem to give you a better answer.