Odds is regularly expressed as F-S, F:S, or F/S - all of which are read as F to S, where F equals the failure to achieve and S equals a success. This is most easily understood because the odds of an event is usually a fraction of overall events, however this is not always the case.
To find odds, one must first determine the probability of an event. Probability of an event occurring is the number of ways an event can occur divided by the total number of possible outcomes. For example, to find the probability of a person in Miami speaking Spanish you would count all of the people in Miami, and then count the Spanish speakers. These numbers then get simplified so 1,404,000/2,400,000 becomes a more manageable 117/200.
Knowing the probability, one can then express the odds. Working with the example, the odds of meeting a Spanish speaker in Miami is 117:83. And if, we continued in our inquiry into the language of Miami resident and found that the probability of a person speaking Creole was 25/200, we could then find the ratio of Spanish to Creole.
The ratio of Spanish speakers to Creole speakers would be 117:25. Having two sets of odds enables the comparison of the two numbers for a better understanding of how the populations compare to one another. This is done without necessarily needing to know about the entire population.