Chance and probability — Mathematics, 7–10 years
Compare how likely different events are, without pretending chance can be predicted exactly.
How likely is it?
Probability is a way to talk about how likely an event is. An event can be impossible, unlikely, equally likely, likely or certain. We can compare chances before trying, but a likely result can still fail once, because chance is not a promise.
Why people measure chance
People faced choices with unknown results: games, weather, travel and harvests. Comparing chances helped them make sensible plans instead of treating every outcome as equally likely. Counting possible results and recording repeated trials gave probability a useful mathematical language.
A bag of counters
A bag holds 3 red counters and 1 blue counter, with no other colours. There are 4 counters altogether, so red has 3 chances out of 4 and blue has 1 chance out of 4. Red is more likely, but blue can still appear. Each draw changes the contents if you do not replace the counter.
Likely does not mean certain
If a red counter is more likely, someone may expect red every time. That is a reasonable feeling because repeated draws usually show more red, but a single draw can still be blue. Probability describes a chance, not a guarantee; only an event with no possible alternative is certain.
Where chance matters
Weather forecasts use observations to estimate the chance of rain, so people can decide whether to take a coat. Games use chance when cards are shuffled or a spinner is turned. Scientists also repeat tests and count results, because one unusual result does not tell the whole story.
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