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Probability tree diagrams show the outcomes and probabilities of a sequence of events, multiplying along branches and adding between them, and are used for combined and conditional probabilities. It's examined right across GCSE and iGCSE Maths. Learn it free on eClassroom through guided worked examples and instantly-marked exam-style questions.
How you do it
Draw a branch for every outcome at each stage and write the probability on it. Multiply along the branches to get the probability of a full path, and add the paths that satisfy the condition. Probabilities on any set of branches from one point add to 1.
Before you start
Best tackled after the AND and OR rules. Later work on problems without replacement assumes it.
What you learn
A tree diagram lays out a two-stage experiment. A tree diagram shows each stage as a set of branches. One multiplication for P(none) beats adding three separate paths. The course works through A probability tree, multiply along, add between and the ‘at least one’ shortcut. Every section has instant-feedback practice questions matched to Edexcel iGCSE 4MA1 and the other major GCSE boards, and the course finishes with full exam-style questions you mark yourself.
Related Topics
Tree Diagrams is part of the Probability strand of our free GCSE maths courses, studied in Higher tier. You work through 3 concepts and 2 worked examples, testing yourself at 3 points. Nearby topics in the same strand are Two-Way Tables, Venn Diagrams, Venn Diagrams & Set Notation and Without Replacement. For unlimited practice, the Probability revision engine builds new questions on demand and records your accuracy.
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