Thus, Probability of E considering F as the sample space = 1
4 ,
or
Probability of E given that the event F has occurred = 1
4
This probability of the event E is called the conditional probability of E given
that F has already occurred, and is denoted by P (E|F) Thus
P(E|F) = 1
4
Note that the elements of F which favour the event E are the common elements of
E and F, i e the sample points of E ∩ F