Odds

Sometimes, probabilities are stated in terms of odds , the ratio of the probability of the event’s occurring to the probability of its not occurring.

Example:

Suppose you roll a six-sided die. Find the odds that you roll a number greater than four.

There are two favorable outcomes ( $5$ and $6$ ), and four unfavorable outcomes $\left(1,2,3,4\right)$ . So the odds are

$\frac{2}{4}=\frac{1}{2}$ ,

or "one-to-two odds" that you will roll a number greater than four.