Answer: 3/6
Step-by-step explanation: the probability of success plus probability of failure equals 1. That is, if 'P' and 'Q' represent the probabilities of an event happening (success) or not (failure) respectively. Thus, P+Q=1.
Since P is given as 3/6, we substitute it into the equation P+Q=1. Therefore, Q=1-P; Q=1-3/6; Q=3/6.