Final answer:
The probability of an event not occurring is found by subtracting the event's probability from 1. If an event's probability is 0.4, then the probability of it not occurring is 0.6.
Step-by-step explanation:
If the probability of an event occurring is 0.4, the probability of the event Not occurring is calculated by subtracting the probability of the event occurring from 1. This is because the sum of the probabilities of all possible outcomes must equal 1. So, the probability of the event Not occurring is 1 - 0.4 = 0.6.