Item 3. (Subadditivity) If A \(\cap\) B = \(\emptyset\text{,}\) then P(A \(\cup\) B) = P(A) + P(B). In general, if {\(A_k\)} are pairwise disjoint then \(P( \cup_k A_k) = \sum_k P(A_k)\text{.}\)