olemus
sündmuse \(A\) tõenäosus \(\mathsf{P}[A|B]\), kui
on toimunud sündmus \(B\)

formaalselt
ühisosa \(A\cap B\) ja sündmuse \(B\) tõenäosuste suhe
\(\mathsf{P}[A|B] = \frac{\mathsf{P}[A\cap B]}{\mathsf{P}[B]}\)

Wiktionary:
the probability that an event will take place given the restrictive assumption that another event has taken place, or that a combination of other events has taken place (Mathematically, the definition would be that the conditional probability of B given A is equal to the joint probability of A and B divided by the probability of A.)

ülevaateid
https://en.wikipedia.org/wiki/Conditional_probability

https://courses.cs.washington.edu/courses/cse312/11au/slides/04cprob.pdf

https://www3.nd.edu/~apilking/Math10120/Lectures/Solutions/Topic11.pdf