P(not A) equals:

In probability theory, the **Complement Rule** states that the sum of the probability of an event occurring and the probability of that event not occurring is always equal to 1. Let $P(A)$ be the probability of event $A$ happening, and $P(\text{not } A)$ (also written as $P(A^c)$ or $P(A')$) be the probability of event $A$ not happening. $$P(A) + P(\text{not } A) = 1$$ To find the formula for $P(\text{not } A)$, we subtract $P(A)$ from both sides of the equation: $$P(\text{not } A) = 1 - P(A)$$ This means that if you know the chance of something happening, you can find the chance of it *not* happening by subtracting it from the whole (1).