Tiny example
A fair coin
A fair coin has two equally likely outcomes.
The probability of heads is 1 out of 2, or 1/2.
Probability
Measuring how likely an outcome is.
Probability gives uncertainty a number. It does not tell you exactly what will happen next, but it helps you reason about what to expect.
Why it matters
Probability helps with games, risk, sampling, statistics, simulation and decisions under uncertainty.
Things to watch for
- Thinking unlikely means impossible.
- Expecting a small sample to look exactly like the long-run probability.
- Adding probabilities when the events should be multiplied.
Where it connects
probabilitytree diagramsstatistics
Try it in a tool
ChanceRepresentation
Probability and Statistics Lab
Explore binomial distributions, sampling and sample means.
ToolChanceRepresentation
GCSE Probability Tree Lab
Build two-stage tree diagrams and compare replacement with no replacement.
ToolChanceRepresentationOptimisation
Monte Carlo Simulator
Estimate pi and area under a curve using random sampling.
Tool and exploration