Recall that

And watch out for the disjoint case!


Example 1


Example 2

Here, is a very common two group problem. Defectives and Non - Defectives

“55 Choose Two”, this is a combination , because we don’t care about order.


Example 3

You could do the math, or since we already know the chances of non being defective, you could just find the other cases (in this case, 1 - (99/118) )


Example 4


Conditional Probability

We say that the probability of A given that B has occurred is

| = Given

On the left of the given, it states the new probability rules to apply On the right of the given, you receive information of what happened previously.

We also have:

And a bit more math, and we get Bayes’ Theorem (Very famous, and important)