Calculating theoretical probabilities from probability trees (two events)
I can calculate and use theoretical probabilities for combined events using probability trees (2 events).
Calculating theoretical probabilities from probability trees (two events)
I can calculate and use theoretical probabilities for combined events using probability trees (2 events).
These resources will be removed by end of Summer Term 2025.
Lesson details
Key learning points
- The probability of an outcome can be found with a probability tree diagram showing all possible outcomes for two events.
- The probability of a set of outcomes can be found using a probability tree diagram.
- The probability of a set of outcomes can be found using a probability tree, even when outcomes are not equally likely.
Keywords
Outcome - An outcome is a result of a trial (e.g. getting heads when flipping a coin once or getting two heads when flipping a coin twice).
Event - An event is a subset of a sample space. i.e. An outcome or set of outcomes that may occur from a trial (e.g. flipping a coin twice and getting the same result each time).
Probability tree - Each branch of a probability tree shows a possible outcome from an event or from a stage of a trial, along with the probability of that outcome happening.
Sample space - A sample space is all the possible outcomes of a trial. A sample space diagram is a systematic way of producing a sample space.
Common misconception
When I see a probability tree, I always multiply the probabilities.
If a probability tree shows a two-stage trial, then the probability of an outcome is the product of the probabilities of the outcomes at each stage. The probability of an event is the sum of the probabilities of each outcome in the event.
To help you plan your year 9 maths lesson on: Calculating theoretical probabilities from probability trees (two events), download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your year 9 maths lesson on: Calculating theoretical probabilities from probability trees (two events), download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
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Explore more key stage 3 maths lessons from the Probability: theoretical probabilities unit, dive into the full secondary maths curriculum, or learn more about lesson planning.
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Lesson video
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Starter quiz
6 Questions
Exit quiz
6 Questions
