In gambling, the chances of winning are often written in terms of odds rather than probabilities. the odds of winning is the ratio of the number of successful outcomes to the number of unsuccessful outcomes. the odds of losing is the ratio of the number of unsuccessful outcomes to the number of successful outcomes. for example, if the number of successful outcomes is 2 and the number of unsuccessful outcomes is 3, the odds of winning are 2: 3 (read "2 to 3") or
two thirds
2
3
. (note: if the odds of winning are
two thirds
2
3
, the probability of success is
two fifths
2
5
.)

the odds of an event occurring are
4
4:
5
5. find (a) the probability that the event will occur and (b) the probability that the event will not occur.