Chance, tree diagrams and the difference between “or” and “and” — tiny words, big mark loss.

Quick Summary

Probability tests logic. Most errors happen because students do not decide whether events are combined with AND or OR.

• ✅ Must-know skills
• ⚠️ Common mistakes

First-Move Decision Flow

• AND or OR?

Exam Practice

• Easy
• Medium
• Hard

Revision Checklist

• [ ] I know when to add and when to multiply.
• [ ] I can complete tree diagrams.
• [ ] I update probabilities without replacement.
• [ ] I can solve at least one questions.
• [ ] I check that probabilities are between 0 and 1.