Bored:Quantities 

"If the variable X is added to the variable Y, the sum is the quantity of X and Y. X cannot equal to Y, ever. So in theory, if two different variables are added, the sum (outcome) of the eqation will be the quantity of both variables, and will NEVER equal to one of the two variables."

You say:
X + Y = Z,  Z never Equals X, Z never Equals Y.

It's faulty:
X = 0
Y = 1
So, X + Y = Z = 1, therefore Z = Y ... hehe.

C.
What you meant to say is:

If any two variables, X, Y, (X,Y != 0) are added, the sum will never equal any one of the two variables.

D.
But, what if we take a person with 3 different ancestries? In theory, if one has 3 different ancestries they are "never just one of the ancestries", however you would qualify such a statement.

So, X + Y + Z = A, A can never equal X, Y, or Z.

Of course here we'd have to add the condition that X, Y, and Z must be > 0. Whereas in Example C, the variables just cannot equal 0.