Work out mutually exclusive events instantly with clear inputs, formula shown and shareable results.
Mutually exclusive events cannot occur together, so their intersection is empty and P(A or B) is simply P(A) + P(B). Their probabilities can never sum to more than 1.
Exclusive union
P(A ∪ B) = P(A) + P(B) when A ∩ B = ∅
Either occurs with probability 0.75 and neither with 0.25.
Only if one has probability zero. Otherwise knowing A occurred tells you B definitely did not, which is dependence.