A card is chosen at random from a standard deck of 52 cards. What is the probability that it is a King or black (or both)?

\(P[\text{king or black}] = P[\text{king}]+P[\text{black}]-P[\text{king and black}]\\ P[\text{king or black}] = \dfrac{4}{52}+\dfrac{26}{52}-\dfrac{2}{52}=\dfrac{28}{52}=\dfrac{7}{13}\)

.