If A and B r independent and
p(AB'UA'B)
given p(A)=p(B)= 0.5
I'm a bit uncertain about your notation, but maybe you want to consider something like
$\displaystyle P((A\cap \overline{B})\cup (\overline{A}\cap B))=P(A\cap \overline{B})+P(\overline{A}\cap B)-P((A\cap\overline{B})\cap(\overline{A}\cap B))=\ldots$
where $\displaystyle P((A\cap\overline{B})\cap(\overline{A}\cap B))=0$, of course. Since A and B are independent, you can easily calculate the remaning probabilities from the probabilities of A and B, respectively.