Answer
Because P (E) + P(not E) = l, then P(not E) = Probability that even E does not occur = 1 - P(E) and P (E) = Probability that even E occurs = 1 -P(not E).
Work Step by Step
Because P (E) + P(not E) = l, then P(not E) = Probability that even E does not occur = 1 - P(E) and P (E) = Probability that even E occurs = 1 -P(not E).