A card is drawn at random from a pack of $52$ cards. What is the probability that the card drawn is either an Ace or a King?

Total cards = $52$ Number of Ace cards $n(A)=4$ Number of King cards $n(K)=4$ Since a card cannot be both an Ace and a King, the events are mutually exclusive: $n(A\cap K)=0$.The number of favorable outcomes for "Ace or King" is:
$$n(A\cup K)=n(A)+n(K)=4+4=8$$
Probability $P(A\cup K)=\frac{8}{52}$ Dividing by $4$:
$$P=\frac{2}{13}$$