If probability of happening of an event is $57%$, then probability of non-happening of the event is

The probability of an event happening is given as $ \displaystyle 57\% $.

Since the total probability of all possible outcomes is always $ \displaystyle 1 $ (or $ \displaystyle 100\% $), the probability of the event not happening is:

$ \displaystyle P(\text{not happening}) = 1 - P(\text{happening}) $

$ \displaystyle = 1 - 0.57 $

$ \displaystyle = 0.43 $