Probability — Mathematics, 11–13 years
Probability measures how likely an event is when the possible outcomes are understood. Mathematics, 11–13 years.
A measure of chance
Probability is a number that describes how likely an event is. Zero means it cannot happen, and one means it must happen; values between them describe uncertainty. It does not tell you exactly what will happen on one try.
Why measure chance?
People needed a fair way to compare uncertain events, especially when games involved bets or shared decisions. If equally likely outcomes are counted, probability gives a clear comparison: favourable outcomes divided by all possible outcomes. The same idea supports predictions from repeated data.
An even number on a die
A fair die has six equally likely results: 1, 2, 3, 4, 5, and 6. Three are even, so the probability of an even result is favourable outcomes ÷ all outcomes = 3 ÷ 6 = 1/2. That is 50%, but one roll can still be odd.
Likely does not mean certain
After several tails, someone may say heads is now due, or after seeing a 50% chance, expect exactly one success in two tries. This feels fair because patterns are easy to notice, but independent trials do not remember the past. Probability describes long-run balance, not a promise about the next result.
Making decisions with uncertainty
Probability appears in weather forecasts, insurance prices, quality checks, sports analysis, and games. It helps compare risks when the possible outcomes and the evidence are clear. A forecast such as 70% rain is useful information, not a promise that rain will fall on every street.
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