Bayes' theorem
How the probability of an event changes with new information?
Let little dashes represent the probabilities of events A and B
A - - -
B - - - -
Only 1 dash is intersecting
If you know A happened, then the probability of B given A becomes
P(B|A) = P(A & B) / P(B) = 1/4
similarly
P(A|B) = P(A & B) / P(A)
Leading to Bayes’ theorem
P(A|B) = P(B|A) P(B) / P(A)