Question

Let $E$ be an event, that $P(notE)$$=$_________

Answer 1

The sum total of the probability of happening of any event $P\left(E\right)$ and the probability of not happening of any event $P(notE)$ is $1$.

For example if we toss a coin the outcomes will either be head or tail. The $P\left(E\right)$ probability of getting a head is $\frac{1}{2}$ and that $P(notE)$ of getting tail or not getting head is $\frac{1}{2}$.

$P\left(E\right)+P(notE)$$=1$

$\frac{1}{2}+\frac{1}{2}=1$

Therefore, to calculate probability of not happening of any event $P(notE)$ we deduct the probability of happening of event $P\left(E\right)$ by $1$. $P(notE)=1-P\left(E\right)$.