Knowledge Organiser: Basic Probability
This topic summary covers Knowledge Organiser: Basic Probability within Basic Probability for GCSE Mathematics. Revise Basic Probability in Probability for GCSE Mathematics with 13 exam-style questions and 20 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 7 of 7 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 7 of 7
Practice
13 questions
Recall
20 flashcards
Knowledge Organiser: Basic Probability
Key Terms
- Probability: A measure of how likely an event is, from 0 to 1
- Outcome: A single possible result of an experiment
- Event: One or more outcomes we are interested in
- Favourable outcome: An outcome that satisfies the event
- Impossible event: An event with probability 0
- Certain event: An event with probability 1
- Equally likely: Each outcome has the same probability
Must-Know Facts
- Probability is always between 0 and 1 (inclusive)
- P = 0 means impossible; P = 1 means certain; P = 0.5 means even chance
- All probabilities for a complete set of outcomes add up to 1
- P(event does NOT happen) = 1 − P(event happens)
- Fractions, decimals, and percentages can all express probability
- A standard die has 6 equally likely outcomes; a deck has 52 cards
- Always simplify probability fractions (e.g. 3/6 = 1/2)
Key Formulas
- P(event) = number of favourable outcomes ÷ total number of possible outcomes
- P(A does not happen) = 1 − P(A)
- Sum of all outcome probabilities = 1
Common Mistakes
- Probability greater than 1: Probability is always between 0 and 1 — if your answer is greater than 1, recheck
- Writing as a fraction then converting incorrectly: P = 3/5 = 0.6 = 60% — all three forms are acceptable unless specified
- Not listing all outcomes: Always count all equally likely outcomes systematically — use a list or sample space diagram
- P(not A) = 1 − P(A) only: This only works if A either happens or doesn't — check there are no other outcomes
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Practice Questions for Basic Probability
Which value represents an impossible event on a probability scale?
Explain what is meant by theoretical probability and state the formula used to calculate it.
Quick Recall Flashcards
13 questions on Basic Probability — practise free
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