To find missing probabilities, there’s a simple idea to remember:

1. Complementary Events: An event is something that can happen, like flipping a coin and getting heads. The complementary event is what doesn’t happen, which in this case would be getting tails.

2. Probability Relationship: The chances of an event and its complement always add up to 1. So, if you know the probability of the event (we can call it $P(A)$), you can find its complement like this:
   $P(A') = 1 - P(A)$

3. Example: Let’s say there’s a 0.3 chance of it raining. You can find out the chance of it not raining like this:
   $P(\text{no rain}) = 1 - 0.3 = 0.7$

Using complementary events helps make probabilities easier to understand!