Let's see... Nothing(subscript1) + Nothing(subscript2) = X.
Consider that nothing equals the absence of everything, therefore Nothing(subscript1) equally the absence of everything.
Since nothing equals the absence of everything, Nothing(subscript2) becomes the absence of Nothing(subscript1), as it is the only thing left to become absent.
So, we now have "The absence of everything" + "The absence of the absence of everything" = X.
The final value of X = Everything.
That's why you see 100%.