If P_{1}, P_{2}, P_{3}, ..., P_{n} are the probabilities of the happening of ‘n’ independent events, then the **(probability that at least one of the events must happen)**

= 1 – Probability of failure of all events

** = 1 – (1 – P**_{1}) (1 – P_{2}) (1 – P_{3}) … (1 – P_{n})