MA35-02 Maths Coming soon
Mutually exclusive events: the addition rule
MA35-02
This lesson is coming soon.
In this lesson
Use P(A or B) = P(A) + P(B) for mutually exclusive events (and the general addition law P(A or B) = P(A) + P(B) - P(A and B) for OCR), correctly choosing addition over multiplication for combined 'or' events.
What it covers
- P(A or B) = P(A) + P(B) for two mutually exclusive events (single events, not sequential/tree events)
- The general (non-mutually-exclusive) addition law P(A or B) = P(A) + P(B) - P(A and B) - OCR only, both tiers
- Drilling 'or' means add across outcomes, contrasted directly against 'and' which means multiply
- Recognising an answer greater than 1 as a signal that addition was used when multiplication was needed
Key words
For: AQA GCSE 8300, Edexcel GCSE 1MA1, Eduqas GCSE C300, Edexcel IGCSE 4MA1, OCR GCSE J560
On the specification
| Board | Spec | Statement |
|---|---|---|
| AQA GCSE 8300 | P4 | Apply the property that the probabilities of an exhaustive set of outcomes sum to 1 |
| Edexcel GCSE 1MA1 | P4 | Apply the property that the probabilities of an exhaustive set of outcomes sum to one; apply the property that the probabilities of an exhaustive set of mutually exclusive events sum to one |
| Eduqas GCSE C300 | FP4 | Apply the property that the probabilities of an exhaustive set of outcomes sum to one; apply the property that the probabilities of an exhaustive set of mutually exclusive events sum to one |
| Eduqas GCSE C300 | HP4 | Apply the property that the probabilities of an exhaustive set of outcomes sum to one; apply the property that the probabilities of an exhaustive set of mutually exclusive events sum to one |
| Edexcel IGCSE 4MA1 | F6.3I | Use the addition rule of probability for mutually exclusive events |
| OCR GCSE J560 | 11.02e | Use the addition law for mutually exclusive events. Use p(A) + p(not A) = 1 |
For teachers
This GCSE Maths lesson teaches mutually exclusive events: the addition rule. By the end, students should be able to use P(A or B) = P(A) + P(B) for mutually exclusive events (and the general addition law P(A or B) = P(A) + P(B) - P(A and B) for OCR), correctly choosing addition over multiplication for combined 'or' events. It works through three worked examples and the mistakes examiners report.