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Life · Guided lesson

Distinguish overlapping from disjoint events

About 11 minutes · 3 reading + 8 practice and checks
Time includes reading, practice, and questions. Extra videos or further study are optional.
See this course’s project requirements

A chance-model packet with a complete sample space, combined-event calculations, conditional probabilities and a repeated-trial comparison.

Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.

What to include

  • List a complete equal-outcome sample space.
  • Calculate a complement and an independent combined event.
  • Audit overlap in an inclusive-or event.
  • Compare conditional and unrestricted denominators.
  • Explain observed frequency versus theoretical chance with all six changed cases.

Review and revise

Use these criteria to check your work and choose what to improve.

  • Method: applies the course-specific rules to the supplied cases with visible intermediate work.
  • Accuracy: results agree with the stated facts, units, boundaries and independent checks.
  • Reasoning: explains why the result follows and identifies a limitation or unresolved question.
  • Transfer: completes changed cases and revises the final project when a relevant assumption changes.
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Before you begin

The idea in everyday life

Case: ten equally likely numbered tokens 1–10. A=even numbers{2,4,6,8,10}; B=numbers above 6{7,8,9,10}.

The idea

For “A or B,” add the separate probabilities and subtract their overlap once. Disjoint events have no overlap. The word “or” in probability includes both unless a problem explicitly says otherwise.

Follow along

Distinguish overlapping from disjoint events — worked practice

For “A or B,” add the separate probabilities and subtract their overlap once. Disjoint events have no overlap. The word “or” in probability includes both unless a problem explicitly says otherwise.

Case: ten equally likely numbered tokens 1–10. A=even numbers{2,4,6,8,10}; B=numbers above 6{7,8,9,10}.

Original practice material

Paste at A1.

AMaterialBSupplied text
CaseCase: ten equally likely numbered tokens 1–10. A=even numbers{2,4,6,8,10}; B=numbers above 6{7,8,9,10}.

Copy as plain text
  1. 1. 1. List

    Write the shared outcomes.

    You should see: Overlap{8,10}: two tokens.

  2. 2. 2. Count

    List the union without duplicate entries.

    You should see: {2,4,6,7,8,9,10}: seven tokens.

  3. 3. 3. Apply

    Calculate the inclusive-or probability.

    You should see: 5/10+4/10−2/10=7/10.

  4. 4. 4. Compare

    Explain what simple addition would count twice.

    You should see: Tokens 8 and 10 appear in both lists.

Now change one thing

On tokens 1–10, A=even and B=numbers above 8. Enter the probability of A or B as a decimal.

Your work

What to finish

An event-union list, overlap count and checked probability.

Common mistake

Watch for this

Inclusive “or” includes all outcomes meeting either condition. An outcome meeting both still belongs, but is counted once.

How can I tell I understand it?

Compute a changed union without assuming “or” excludes outcomes meeting both conditions.

Try 3 questions

Quick knowledge check

Answer all 3 questions. Get at least 2 right and the lesson completes automatically.

Not yet passed

You’ll get an explanation for each answer. Signed in? Your results save to your account.

1P(A)=0.4, P(B)=0.5, P(both)=0.2. What is P(A or B)?
2Drawing one token that is red or blue, with every token exactly one color, is which relationship?
3Why does “even or above 6” include token 8?
0 of 3 answeredApply the lesson to a short question, then review the explanation.
4
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Answer all 3 questions above and get at least 2 right. You can review the explanations and try again.

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Sources and further reading

Explore the references behind this lesson.

OpenStax: independent and mutually exclusive events
Source & access notes · checked 2026-10-01

Web open/search showed the official page, its topic heading and relevant concept description. This is a content/source check, not a provider endorsement.

Access: Official page retrieved with the web reader on 2026-10-01; interactive tools and videos were not certified by retrieval.

Reuse: Original fictional teaching cases, calculations, questions and examples; link and short factual paraphrase only. No copied source exercises or illustrations.

OpenStax: probability rules
Source & access notes · checked 2026-10-01

Web open/search showed the official page, its topic heading and relevant concept description. This is a content/source check, not a provider endorsement.

Access: Official page retrieved with the web reader on 2026-10-01; interactive tools and videos were not certified by retrieval.

Reuse: Original fictional teaching cases, calculations, questions and examples; link and short factual paraphrase only. No copied source exercises or illustrations.

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