Maths Literacy Matric Revision: Mutually exclusive events

Revision Notes: Probability – Mutually Exclusive Events (Grade 12 CAPS Mathematical Literacy)


Probability is fundamental to understanding the likelihood of various events occurring. One specific type of probability is related to mutually exclusive events. These concepts will help you tackle real-world problems, make informed decisions, and understand the mathematical principles underlying randomness and chance.

Learning objectives:

  • Understand the definition and characteristics of mutually exclusive events.
  • Apply the addition rule for calculating probabilities of mutually exclusive events.
  • Identify common misconceptions and errors.
  • Practice solving problems involving mutually exclusive events.

Key Points

  1. Definition and Characteristics:

    • Mutually Exclusive Events: Two events are mutually exclusive if they cannot happen at the same time. For example, when you throw a dice, getting a 3 and a 5 in the same toss is impossible because they are mutually exclusive.
    • Addition Rule: For mutually exclusive events, the probability of either event occurring is the sum of their individual probabilities.
      P(A \text{ or } B) = P(A) + P(B)
      provided that (A) and (B) are mutually exclusive.
  2. Probability Basics:

    • Probability Scale: The probability of any event ranges between 0 and 1 (or 0% to 100%). An event with a probability of 0 is impossible, while an event with a probability of 1 is certain.
    • Notation: Probability of event (A) is denoted by (P(A)).

Real-World Applications

Example 1:

Consider a bag with 4 red balls and 6 blue balls. If one ball is selected at random, calculate the probability of selecting either a red or a blue ball.

Since selecting a red ball and a blue ball are mutually exclusive events:
[ P(\text{Red or Blue}) = P(\text{Red}) + P(\text{Blue}) ]

[ P(\text{Red}) = \frac{4}{10} = 0.4 ]
[ P(\text{Blue}) = \frac{6}{10} = 0.6 ]
[ P(\text{Red or Blue}) = 0.4 + 0.6 = 1 ]

Solution Steps:

  1. Identify the total number of outcomes.
  2. Confirm if the events are mutually exclusive.
  3. Apply the addition rule.

Common Misconceptions and Errors

  • Ignoring Mutual Exclusivity: Assuming events are mutually exclusive when they are not can lead to errors. Always check if events can occur simultaneously.
  • Incorrect Probabilities Summation: Adding probabilities that should be subtracted if events are not mutually exclusive.

Strategy to Avoid Errors:

  • Clarify Event Relations: Always explicitly confirm if events are mutually exclusive.
  • Double-check Calculations: Before finalizing your answer, review if addition or other operations are suitably applied.

Practice and Review

Practice Problems:

  1. A deck of cards has 52 cards. What is the probability of drawing a King or a Queen from a well-shuffled deck?
  2. There are 5 green, 3 blue, and 2 red marbles in a jar. What is the probability of picking either a blue or a red marble?


  1. Mutually exclusive since a card cannot be both a King and a Queen:
  2. ( P(\text{King}) = \frac{4}{52} = 0.077 )
  3. ( P(\text{Queen}) = \frac{4}{52} = 0.077 )
  4. ( P(\text{King or Queen}) = 0.077 + 0.077 = 0.154 )

  5. Mutually exclusive since a marble cannot be blue and red at the same time:

  6. Total marbles = 10
  7. ( P(\text{Blue}) = \frac{3}{10} )
  8. ( P(\text{Red}) = \frac{2}{10} )
  9. ( P(\text{Blue or Red}) = \frac{3}{10} + \frac{2}{10} = 0.5 )

Examination Tips

  • Keywords: Focus on terms like “either”, “or”, and “mutually exclusive” in exam questions.
  • Time Management: Allocate time to review answers, ensure steps are logically correct, and recheck calculations.

Connections and Extensions

  • Conditional Probability: Not mutually exclusive events often involve conditional probability. Revisiting this helps in understanding complex scenarios.
  • Real-life Situations: Recognize mutually exclusive events in daily life (e.g., rain or no rain).

Summary and Quick Review

  • Mutually Exclusive Events: Cannot occur simultaneously.
  • Addition Rule:
    P(A \text{ or } B) = P(A) + P(B)
  • Application in Real Life: Use this understanding to determine probabilities in everyday situations and data analysis.

Additional Resources

  • Videos: Search for educational videos on probability and mutually exclusive events on Khan Academy and other educational platforms.
  • Practice Platforms: Online quizzes on platforms like Quizlet help enforce learning.

For a more detailed study, refer to your CAPS Mathematical Literacy textbook and practice problem sections【4:0†source】【4:1†source】【4:2†source】.

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