Mathematicscalendar_todayLast updated: Apr 2026
What is Probability?
/ˌprɒbəˈbɪlɪti/
Probability is a measure of how likely an event is to occur, expressed as a number between 0 (impossible) and 1 (certain), or equivalently as a percentage between 0% and 100%.
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Everyday Example
A fair coin has a 0.5 (50%) probability of landing heads. A weather forecast of "70% chance of rain" means that in similar conditions historically, it rained 7 times in 10.
publicReal-World Application
“Probability theory underpins insurance pricing, financial risk models, medical trial design, weather forecasting, and all of machine learning.”
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Did you know?
Modern probability theory was developed by Blaise Pascal and Pierre de Fermat in 1654, originally to solve gambling problems posed by a French nobleman.
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Key Insight
Humans are notoriously bad at intuitive probability. We overweight vivid, recent events (the availability heuristic) and underestimate the role of chance in everyday outcomes.
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