Year 10 Mathematics Lesson

Mutually Exclusive Events: From Definition to Combined Probability

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Year 10 (approximately 9th–10th Grade, age 14–15)BTC Style / Thinking Classrooms50 min

Learning Objective

Students will identify mutually exclusive events and apply the Addition Rule P(A or
B) = P(A) + P(B) to calculate probabilities, extending to P(A orB) = P(A) + P(B) − P(A andB) for non-mutually-exclusive events.

Lesson Overview

Students move from identifying whether two events can occur simultaneously to calculating combined probabilities using the Addition Rule, including non-mutually-exclusive events as the ceiling extension.

Materials

Vertical whiteboards or large paper
Dry-erase markers
Pencil and paper

Scaffolded Task Progression

1Task 1

A fair six-sided die is rolled. Event A: rolling a 2. Event B: rolling a 5.

Can A and B both happen on the same roll? List the sample space and circle any outcomes shared by both events.

2Task 2

A fair six-sided die is rolled. Event A: rolling an even number. Event B: rolling an odd number.

Are A and B mutually exclusive? Justify using the sample space.

3Task 3

A fair six-sided die is rolled. Event A: rolling an even number. Event B: rolling a number greater than 3.

Are A and B mutually exclusive? Justify using the sample space.

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