number of results giving the event
total number of possible results
It is a number between 0 and 1 inclusive.
The probability P(A+B) that at least one of the events A and B
occurs is given by:
P(A+B) < or = P(A) + P(B)
where P(A) and P(B) are the probabilities of A and B respectively. The
equality applies if events A and B are exclusive, i.e. the
occurrence of one precludes the other.
The probability P(AB) of obtaining both A and B is given by:
P(AB) = P(A/B)P(B) [or P(B/A)P(A)]
where P(A/B) is the probability of A occurring, given that B has
If A and B are independent, P(AB) = P(A)P(B).
© 1999, 2000 The University of Liverpool,
Department of Physics
funded by The Engineering and
Physical Sciences Research Council
and maintained by the MATTER Project