Complementary events are pairs of outcomes where one thing happens only if the other one doesn't. Here are some easy examples from everyday life:

1. Coin Toss:

   • Event A: You get heads.
   • Complement: You get tails.

2. Weather:

   • Event A: It rains today.
   • Complement: It does not rain today.

To figure out the chances of these events, you can use a simple formula.

If you know the chance of an event happening, like $P(A)$, you can find the chance of the opposite event (the complement) with this:

$$P(A') = 1 - P(A)$$

In this formula, $A'$ is the opposite of event $A$.

For example, if the chance of it raining today is $P(A) = 0.3$, then the chance of it not raining is:

$$P(A') = 1 - 0.3 = 0.7$$

So, there’s a 70% chance that it won't rain today.