As the number of trials in a probability simulation increases (e.g., from 10 to 10,000), what generally happens to the observed relative frequency of an event?

If ${P(A) = 0.5}$, ${P(B) = 0.4}$, and ${P(A \cup B) = 0.9}$, then events and must be:

In the coin-flipping game between Peter and Eliott, what is the probability that Eliott wins on his second turn? This occurs if the first three flips (Peter, Eliott, Peter) are all Tails and the fourth flip (Eliott's second turn) is a Head.

Which set-builder notation correctly represents the set $K = \{1, 4, 9, 16, 25\}$?

True or False: If three events $A$, $B$, and $C$ are mutually exclusive and cover the entire sample space $S$, then their probabilities must sum to 1.