1. The problem asks: If two events are collectively exhaustive, what is the probability that one or the other occurs? 2. **Definition:** Two events are collectively exhaustive if at least one of the events must occur, meaning their combined probability covers the entire sample space. 3. The formula for the probability of the union of two events $A$ and $B$ is: $$P(A \cup B) = P(A) + P(B) - P(A \cap B)$$ 4. Since the events are collectively exhaustive, the probability that either event $A$ or event $B$ occurs is 1, because together they cover all possible outcomes. 5. Therefore, the answer is: $$P(A \cup B) = 1.00$$ 6. The correct choice is (c) 1.00. This means that when two events are collectively exhaustive, the probability that one or the other occurs is always 1, as they cover the entire sample space.