Probability is the measure of how likely an event will happen. Probability is usually expressed as a fraction or a decimal.

Odds show how the chance of an event happening compares to the chance of the event not happening. Odds are usually expressed as a ratio.

Odds of an event =
Number of outcomes where the event happens : Number of outcomes where the event does not happen

Example 1: Rolling dice

A die (or one "dice") is rolled. What is the probability of rolling a 4?

When a die is rolled, you can get only 6 possible outcomes: 1, 2, 3, 4, 5, and 6.

Probability of rolling a 4 = P(rolling a 4) = =

A die is rolled. What are the odds of rolling a 4?

Odds of rolling a 4 =
Number of outcomes where you roll a 4 : Number of outcomes where you do not roll a 4
Odds of rolling a 4 = 1 : 5

Example 2: Highlighted pieces

Find the probability that a randomly selected piece of the shape will be highlighted and find the odds that a piece chosen will not be highlighted. Express probabilities as a simplified fraction and odds as a ratio of two numbers with no common factors other than 1 (i.e. "2:1").

Probability: Odds:

P(selecting a highlighted piece) = = = =

Odds that a selected piece will not be highlighted =

Number of outcomes where a selected piece is not highlighted	:	Number of outcomes where a selected piece is highlighted
Number of unhighlighted pieces	:	Number of highlighted pieces
4	:	2

The odds 4:2 can be simplified to 2:1.

So the answer is Probability: Odds: