# A Quick Guide to Bayes’ Theorem

Mr Smith has two children. At least one of them is a girl. What is the probability that both children are girls?

If you said 1/2 then you are not correct! As you will see, the actual answer is 2/3.

Bayes’ theorem describes the probability of something happening based on prior information about the event. It can also be interpreted as an approach for expressing the degree to which…