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Math & Optimization · beginner · concept 55 of 311 · Updated Nov 4, 2026

Probability & Bayes' Theorem

Machine learning is applied probability: models output distributions, training maximizes likelihood, and Bayes' theorem tells you how to update belief when evidence arrives. It is also the antidote to the classic diagnostic fallacy, a positive test for a rare disease usually still means you are fine.

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Key terms

Conditional probabilityPrior and posteriorLikelihoodDistributionsExpectation

Where you meet it in the real world

Spam filters, medical diagnosis, language model sampling, risk models, A/B test analysis