What are the odds of a mob in minecraft dropping all 4 peices of armor that it is wearing?

There's a 5% chance that any armor will drop, and the only way to change that is to create a custom mob. Also, looting doesn't affect chances of a mob's armor dropping. Mob armor never drops with full durability, most likely it will be broken before it is dropped. And, rare drops occur 2.5% of the time. There are 6 possible rare drops from a zombie, 4 of which are armour, which I will assume have the same chance of happening. Therefore the percentage of zombies that will drop a piece of armour is 1.67%, or a chance of 0.0167.