Homeschool Guide: These lesson plans are a guide for parents. Content may contain errors — always cross-reference with official exam board specifications.

P9: Conditional Probability

FoundationHigherAll Boards

4 detailed 50-minute lessons with teaching scripts, worked examples, parent guides, and assessment criteria.

Fastmail

Lesson Overview

Total Lessons: 4
Tier: Foundation and Higher
Duration: 50 minutes per lesson (200 minutes total)
Exam Boards: AQA, Edexcel, OCR, Eduqas, CCEA

Learning Objectives

Prerequisites

Materials & Equipment

Lesson 1: Introduction: Conditional Probability

Duration: 50 minutes

Starter Activity (5 minutes)

Quick Recall

3 quick questions to activate prior knowledge about conditional probability. Use mini-whiteboard or paper.

Main Content (35 minutes)

Parent/Teacher Guide:
Before lesson: Read script below. Prepare materials. Pre-teach key vocab: P9.
If stuck: See Troubleshooting below. Break into smaller steps.
Extension: See Stretch & Challenge section.
Teaching Script (35 mins):
Mins 0-5 - Hook: "Today: Conditional Probability. Goal: by the end you can in a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English), using the method shown step by step. Connects to the previous lesson in this unit because you'll reuse its method throughout today's work."
Mins 5-15 - Direct Instruction: 1) Define: "Conditional Probability is..." 2) Key principle: "Most important:..." 3) Draw diagram, label live. 4) Real example: "Like In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English). - a real example worked through in full..."
Mins 15-25 - Guided Practice: Ex1: Teacher models. Ex2: Student tries with guidance. Ex3: Student independent.
Mins 25-35 - Independent Practice: 3-5 questions. Immediate feedback.
Worked Example 1: Basic

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  1. What is asked? In
  2. Recall knowledge: P(A|B) = P(A ∩ B) ÷ P(B) — vertical bar reads "given that"; Multiplication rule: P(A ∩ B) = P(A|B) × P(B)
  3. Apply:
  4. Check: Check the units named in the question and sense-check the size of your answer.
  5. Answer: State the complete final answer.

Tip: "Show working - method marks > answer marks."

Worked Example 2: Multi-step

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  1. Break down: Separate parts?
  2. Solve each:
  3. Combine: The parts chain: each answer feeds the next step of the question.
  4. Final answer: Evidence cited from the lesson content.
Worked Example 3: Data/Application

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  1. Read data: Axes, units, scale
  2. Patterns: Trends, anomalies
  3. Explain: Why? Using conditional probability
  4. Conclude: Evidence-based

Common Questions & Troubleshooting

Q: "Why does P(A|B) = P(A ∩ B) ÷ P(B) — vertical bar reads "given that" work this way?"
A: Analogy: "In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).". Try re-draw or re-write the worked example from memory, then check it against the model answer.
Q: "Wrong answers on calculations."
A: Checklist: units? formula? calculator mode? sig figs?
Q: "Can't remember key terms."
A: Flashcards (term front, def+diagram back). Spaced repetition: day 1, 3, 7.
Q: "Exam wording confuses me."
A: Commands: Describe=what you see; Explain=reasons; Evaluate=pros/cons+judgement; Calculate=working+units.
Q: "Running out of time."
A: 1 mark/min. Skip hard, return. Attempt all - partial marks count.

Assessment & Model Answers

Mastery Checklist:
  • [ ] Define Conditional Probability in own words
  • [ ] Identify features in diagram
  • [ ] Explain process step-by-step
  • [ ] Apply to unfamiliar context
  • [ ] Score 80%+ on past paper question

Model Answer: Past Paper Question

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  • 1 mark: [Key terminology]
  • 1 mark: [Mechanism/process]
  • 1 mark: [Application/example]
  • 1 mark: [Evaluation - Higher]

Model response: "[Complete answer with expected detail/terminology]"

Why full marks: [What makes this strong]

Stretch & Challenge (Grade 8-9):
  • Synoptic links: Connect to P8-tree-diagrams / the next lesson
  • Real-world: Research use in industry, medicine or research
  • Advanced calc: Try a more challenging variant
  • Critical: "Evaluate limitations of today's model"
  • Research: Recent discovery on conditional probability, summarise 100 words

Plenary (5 mins)

Label the Diagram

Unlabelled diagram - write all parts in 1 min

Assessment Criteria

Lesson 2: Core Concepts: Conditional Probability

Duration: 50 minutes

Starter Activity (5 minutes)

Review Previous Lesson

Quick recap: write 3 key points from last lesson on conditional probability. Use mini-whiteboard or paper.

Main Content (35 minutes)

Parent/Teacher Guide:
Before lesson: Read script below. Prepare materials. Pre-teach key vocab: P9.
If stuck: See Troubleshooting below. Break into smaller steps.
Extension: See Stretch & Challenge section.
Teaching Script (35 mins):
Mins 0-5 - Hook: "Today: Conditional Probability. Goal: by the end you can in a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English), using the method shown step by step. Connects to the previous lesson in this unit because you'll reuse its method throughout today's work."
Mins 5-15 - Direct Instruction: 1) Define: "Conditional Probability is..." 2) Key principle: "Most important:..." 3) Draw diagram, label live. 4) Real example: "Like In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English). - a real example worked through in full..."
Mins 15-25 - Guided Practice: Ex1: Teacher models. Ex2: Student tries with guidance. Ex3: Student independent.
Mins 25-35 - Independent Practice: 3-5 questions. Immediate feedback.
Worked Example 1: Basic

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  1. What is asked? In
  2. Recall knowledge: P(A|B) = P(A ∩ B) ÷ P(B) — vertical bar reads "given that"; Multiplication rule: P(A ∩ B) = P(A|B) × P(B)
  3. Apply:
  4. Check: Check the units named in the question and sense-check the size of your answer.
  5. Answer: State the complete final answer.

Tip: "Show working - method marks > answer marks."

Worked Example 2: Multi-step

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  1. Break down: Separate parts?
  2. Solve each:
  3. Combine: The parts chain: each answer feeds the next step of the question.
  4. Final answer: Evidence cited from the lesson content.
Worked Example 3: Data/Application

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  1. Read data: Axes, units, scale
  2. Patterns: Trends, anomalies
  3. Explain: Why? Using conditional probability
  4. Conclude: Evidence-based

Common Questions & Troubleshooting

Q: "Why does P(A|B) = P(A ∩ B) ÷ P(B) — vertical bar reads "given that" work this way?"
A: Analogy: "In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).". Try re-draw or re-write the worked example from memory, then check it against the model answer.
Q: "Wrong answers on calculations."
A: Checklist: units? formula? calculator mode? sig figs?
Q: "Can't remember key terms."
A: Flashcards (term front, def+diagram back). Spaced repetition: day 1, 3, 7.
Q: "Exam wording confuses me."
A: Commands: Describe=what you see; Explain=reasons; Evaluate=pros/cons+judgement; Calculate=working+units.
Q: "Running out of time."
A: 1 mark/min. Skip hard, return. Attempt all - partial marks count.

Assessment & Model Answers

Mastery Checklist:
  • [ ] Define Conditional Probability in own words
  • [ ] Identify features in diagram
  • [ ] Explain process step-by-step
  • [ ] Apply to unfamiliar context
  • [ ] Score 80%+ on past paper question

Model Answer: Past Paper Question

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  • 1 mark: [Key terminology]
  • 1 mark: [Mechanism/process]
  • 1 mark: [Application/example]
  • 1 mark: [Evaluation - Higher]

Model response: "[Complete answer with expected detail/terminology]"

Why full marks: [What makes this strong]

Stretch & Challenge (Grade 8-9):
  • Synoptic links: Connect to P8-tree-diagrams / the next lesson
  • Real-world: Research use in industry, medicine or research
  • Advanced calc: Try a more challenging variant
  • Critical: "Evaluate limitations of today's model"
  • Research: Recent discovery on conditional probability, summarise 100 words

Plenary (5 mins)

Label the Diagram

Unlabelled diagram - write all parts in 1 min

Assessment Criteria

Lesson 3: Application: Conditional Probability

Duration: 50 minutes

Starter Activity (5 minutes)

Review Previous Lesson

Quick recap: write 3 key points from last lesson on conditional probability. Use mini-whiteboard or paper.

Main Content (35 minutes)

Parent/Teacher Guide:
Before lesson: Read script below. Prepare materials. Pre-teach key vocab: P9.
If stuck: See Troubleshooting below. Break into smaller steps.
Extension: See Stretch & Challenge section.
Teaching Script (35 mins):
Mins 0-5 - Hook: "Today: Conditional Probability. Goal: by the end you can in a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English), using the method shown step by step. Connects to the previous lesson in this unit because you'll reuse its method throughout today's work."
Mins 5-15 - Direct Instruction: 1) Define: "Conditional Probability is..." 2) Key principle: "Most important:..." 3) Draw diagram, label live. 4) Real example: "Like In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English). - a real example worked through in full..."
Mins 15-25 - Guided Practice: Ex1: Teacher models. Ex2: Student tries with guidance. Ex3: Student independent.
Mins 25-35 - Independent Practice: 3-5 questions. Immediate feedback.
Worked Example 1: Basic

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  1. What is asked? In
  2. Recall knowledge: P(A|B) = P(A ∩ B) ÷ P(B) — vertical bar reads "given that"; Multiplication rule: P(A ∩ B) = P(A|B) × P(B)
  3. Apply:
  4. Check: Check the units named in the question and sense-check the size of your answer.
  5. Answer: State the complete final answer.

Tip: "Show working - method marks > answer marks."

Worked Example 2: Multi-step

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  1. Break down: Separate parts?
  2. Solve each:
  3. Combine: The parts chain: each answer feeds the next step of the question.
  4. Final answer: Evidence cited from the lesson content.
Worked Example 3: Data/Application

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  1. Read data: Axes, units, scale
  2. Patterns: Trends, anomalies
  3. Explain: Why? Using conditional probability
  4. Conclude: Evidence-based

Common Questions & Troubleshooting

Q: "Why does P(A|B) = P(A ∩ B) ÷ P(B) — vertical bar reads "given that" work this way?"
A: Analogy: "In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).". Try re-draw or re-write the worked example from memory, then check it against the model answer.
Q: "Wrong answers on calculations."
A: Checklist: units? formula? calculator mode? sig figs?
Q: "Can't remember key terms."
A: Flashcards (term front, def+diagram back). Spaced repetition: day 1, 3, 7.
Q: "Exam wording confuses me."
A: Commands: Describe=what you see; Explain=reasons; Evaluate=pros/cons+judgement; Calculate=working+units.
Q: "Running out of time."
A: 1 mark/min. Skip hard, return. Attempt all - partial marks count.

Assessment & Model Answers

Mastery Checklist:
  • [ ] Define Conditional Probability in own words
  • [ ] Identify features in diagram
  • [ ] Explain process step-by-step
  • [ ] Apply to unfamiliar context
  • [ ] Score 80%+ on past paper question

Model Answer: Past Paper Question

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  • 1 mark: [Key terminology]
  • 1 mark: [Mechanism/process]
  • 1 mark: [Application/example]
  • 1 mark: [Evaluation - Higher]

Model response: "[Complete answer with expected detail/terminology]"

Why full marks: [What makes this strong]

Stretch & Challenge (Grade 8-9):
  • Synoptic links: Connect to P8-tree-diagrams / the next lesson
  • Real-world: Research use in industry, medicine or research
  • Advanced calc: Try a more challenging variant
  • Critical: "Evaluate limitations of today's model"
  • Research: Recent discovery on conditional probability, summarise 100 words

Plenary (5 mins)

Exam Question Speed Round

5 quick questions, 1 min each. Mark together.

Assessment Criteria

Lesson 4: Exam Practice: Conditional Probability

Duration: 50 minutes

Starter Activity (5 minutes)

Review Previous Lesson

Quick recap: write 3 key points from last lesson on conditional probability. Use mini-whiteboard or paper.

Main Content (35 minutes)

Parent/Teacher Guide:
Before lesson: Read script below. Prepare materials. Pre-teach key vocab: P9.
If stuck: See Troubleshooting below. Break into smaller steps.
Extension: See Stretch & Challenge section.
Teaching Script (35 mins):
Mins 0-5 - Hook: "Today: Conditional Probability. Goal: by the end you can in a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English), using the method shown step by step. Connects to the previous lesson in this unit because you'll reuse its method throughout today's work."
Mins 5-15 - Direct Instruction: 1) Define: "Conditional Probability is..." 2) Key principle: "Most important:..." 3) Draw diagram, label live. 4) Real example: "Like In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English). - a real example worked through in full..."
Mins 15-25 - Guided Practice: Ex1: Teacher models. Ex2: Student tries with guidance. Ex3: Student independent.
Mins 25-35 - Independent Practice: 3-5 questions. Immediate feedback.
Worked Example 1: Basic

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  1. What is asked? In
  2. Recall knowledge: P(A|B) = P(A ∩ B) ÷ P(B) — vertical bar reads "given that"; Multiplication rule: P(A ∩ B) = P(A|B) × P(B)
  3. Apply:
  4. Check: Check the units named in the question and sense-check the size of your answer.
  5. Answer: State the complete final answer.

Tip: "Show working - method marks > answer marks."

Worked Example 2: Multi-step

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  1. Break down: Separate parts?
  2. Solve each:
  3. Combine: The parts chain: each answer feeds the next step of the question.
  4. Final answer: Evidence cited from the lesson content.
Worked Example 3: Data/Application

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  1. Read data: Axes, units, scale
  2. Patterns: Trends, anomalies
  3. Explain: Why? Using conditional probability
  4. Conclude: Evidence-based

Common Questions & Troubleshooting

Q: "Why does P(A|B) = P(A ∩ B) ÷ P(B) — vertical bar reads "given that" work this way?"
A: Analogy: "In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).". Try re-draw or re-write the worked example from memory, then check it against the model answer.
Q: "Wrong answers on calculations."
A: Checklist: units? formula? calculator mode? sig figs?
Q: "Can't remember key terms."
A: Flashcards (term front, def+diagram back). Spaced repetition: day 1, 3, 7.
Q: "Exam wording confuses me."
A: Commands: Describe=what you see; Explain=reasons; Evaluate=pros/cons+judgement; Calculate=working+units.
Q: "Running out of time."
A: 1 mark/min. Skip hard, return. Attempt all - partial marks count.

Assessment & Model Answers

Mastery Checklist:
  • [ ] Define Conditional Probability in own words
  • [ ] Identify features in diagram
  • [ ] Explain process step-by-step
  • [ ] Apply to unfamiliar context
  • [ ] Score 80%+ on past paper question

Model Answer: Past Paper Question

Q: In a class of 30 students: 18 study Maths, 12 study English, 6 study both. Find P(studies Maths | studies English).

  • 1 mark: [Key terminology]
  • 1 mark: [Mechanism/process]
  • 1 mark: [Application/example]
  • 1 mark: [Evaluation - Higher]

Model response: "[Complete answer with expected detail/terminology]"

Why full marks: [What makes this strong]

Stretch & Challenge (Grade 8-9):
  • Synoptic links: Connect to P8-tree-diagrams / the next lesson
  • Real-world: Research use in industry, medicine or research
  • Advanced calc: Try a more challenging variant
  • Critical: "Evaluate limitations of today's model"
  • Research: Recent discovery on conditional probability, summarise 100 words

Plenary (5 mins)

Exam Question Speed Round

5 quick questions, 1 min each. Mark together.

Assessment Criteria

📝 Mark Scheme Guidance

How examiners mark P9: Read the command word carefully — State = one word/phrase (1 mark), Describe = pattern or detail (2 marks), Explain = reason with "because" (2–3 marks), Compare = similarities AND differences, Evaluate = both sides + conclusion. Method marks are awarded for correct working even if the final answer is wrong. Always show your working — unexplained answers score zero for AO2.

Success on P9 questions: Underline the command word, count the marks (one mark per point expected), and answer in the format the command word demands.

Board Notes & Revision Links

This lesson is examined by: AQA 8300 | Edexcel 1MA1 | OCR J560 | Eduqas C300 | CCEA M-units. Tier and paper details vary - always check your board's current specification.

Follow-up revision: P9-conditional-probability on GCSE Revise (notes, flashcards and auto-graded target tests for this exact topic).

📐 Reference Diagram

START Condition true? Yes No Do A Do B

✏️ Draw-Along Instructions

Parent/teacher: Draw the key diagram for probability: start with the main structure, add labels with arrows, then annotate with the key facts from the lesson. Use a ruler for straight lines.

Display the reference diagram (or draw it live) while pupils copy. Check each label as it is added.

Homework & Consolidation

Recommended Resources

🎓 Smart Lesson (Guided)