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Theoretical Probability

Theoretical probability is found by dividing the number of favourable outcomes by the total number of equally likely outcomes.

Practice This Concept

Main explanation

Teacher explanation

This method is used when all outcomes have the same chance, such as faces of a fair die or heads and tails of a fair coin. The word equally likely is important.

Example

For a fair die, probability of getting an even number is 3/6 = 1/2.

Simple analogy

Favourable means matching the event, not just liked by the student.

Common confusion

Students forget to check equal likelihood and apply the formula to unfair or uneven situations.

Exam tip

First list total equally likely outcomes, then count only the outcomes that satisfy the event.

Study the theoretical probability diagram carefully

Use the labelled diagram to keep theoretical probability clear in short answers and revision.

What this diagram makes clear

This diagram keeps the labels and direction of theoretical probability in the right order.

Where this helps in exams

Use this for labelled diagram work and short exam answers on theoretical probability.

Revision cue

Revise theoretical probability through the labels before writing the answer.

Answer writing and exam use

1-mark use

Write the exact meaning of theoretical probability in one clean line.

2-mark use

Define theoretical probability and add one example or condition.

3-mark use

Explain theoretical probability, show the method or example, and mention the common mistake.

MCQ Quiz

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