Equally likely (or mutually symmetrical or equi-probable) event are defined to be a set of events if after taking into consideration all relevant evidence one cannot be expected to occur in perfernce to any other. For example tail are equally likely. On the other hand if an unbiased coin is tossed twice (or two unbiased coins) then the three event A0 , A1 and A2 where Ai denotes n(A0) = 1, n(A1) = 2,(A2) = 1 where n(Ai) denotes the number of times the event A1 occurs .