in other words, the union of A and B is given by the union of all the outcomes in A with all the outcomes in B that are not in B. To estimate the probability of an event A, rep...in other words, the union of A and B is given by the union of all the outcomes in A with all the outcomes in B that are not in B. To estimate the probability of an event A, repeat the random experiment several times (each repetition is called a trial) and count the number of times A occurred, i.e., the number of times the resulting outcome is in A.