Suppose s and t are mutually exclusive events, p(s)=22% and p(t)=47%. find p(s or t).

since s and t are mutually exclusive, their probabilities are disjoint and we have that p(s and t) = p(s ∩ t) = 0.

this equation gives you the intersection (or) of the probability of two mutually disjoint events: p(s or t) = p(s ∪ t) = p(a) + p(b) = 22% + 47% = 69%

shorter then the tree