So in your example, the odds are 7:3. In English, that means that if we had a horse race and we held 10 races with the same horses, our favored horse would finish first 7 times and lose the remaining three. But treated as a probability? If we look at it that way, we have 10 possible outcomes and the event of interest (the horse winning) happens 70% of the time. Conversely, the probability of the event not happening (the horse losing) is 30%.
