Probability is a measure of likelihood. It quantifies the chance of an event occurring.

Experimental probability is calculated by the frequency of an event occurring based on repeated trials.

Theoretical probability is determined by systematically finding all the possible outcomes of an experiment (the sample space).

The number of favourable outcomes is compared to all the possible outcomes to express the probability as a fraction, decimal, percentage or ratio. 

The more trials within an experiment the more experimental probability aligns to theoretical probability.

Randomness is the unpredictability of an outcome occurring.

 It is not possible to predict which outcome in a trial will occur because randomness is not influenced by any factor other than chance.

Outcomes are fair when there is an equal chance of occurrence.

A weighted dice is not 'fair' because the possible outcomes do not have an equal chance of occurring.

Biased outcomes do not have an equal chance of occurrence. 

They are not fair.

An independent event is an event that is not affected by the outcome of another event.

A dependent event is an event that is affected by the outcome of a prior event.

The probability of events can be described using language and/or numerical terms.

• Language descriptions

• Numerical descriptions

• Experiment

• Trial

• Outcome

• Frequency

• Sample space

• Event

For more information, please refer to page 46.

There are several ways to systematically determine the number of possible outcomes (i.e. sample space) for situations involving elements of chance.

• Systematic list

• Tree diagram

• Table

For more information, please go to pages 46-47.

• Subjective judgements

• Recency effect

• Independence effect

• Sampling variability effect

• Equi-probability bias

• Outcomes equal events confusion

For more information, please refer to page 47.