1. The problem is to find the probability of "at least one event" occurring in a given set of events. 2. The formula to calculate the probability of at least one event happening is: $$P(\text{at least one}) = 1 - P(\text{none})$$ This means we subtract the probability that none of the events occur from 1. 3. To apply this, first calculate the probability that none of the events happen (i.e., all events fail). 4. Then subtract that value from 1 to get the probability that at least one event occurs. 5. This approach is often easier than summing the probabilities of each event individually, especially when events are independent. 6. For example, if you have $n$ independent events each with probability $p_i$ of occurring, then: $$P(\text{none}) = \prod_{i=1}^n (1 - p_i)$$ and $$P(\text{at least one}) = 1 - \prod_{i=1}^n (1 - p_i)$$ This formula gives the probability that at least one event happens among the $n$ events.