Probability & statistics Introduction
Probability
Express uncertainty with numbers between zero and one.
Before this
No earlier lesson needed. Start here.
The intuition
Probability describes how likely an event is under a model of uncertainty. Mutually exclusive outcomes that cover every possibility have probabilities adding to one.
A concrete example
A fair six-sided die has probability 1/6 for each face. Rolling an even number has probability 3/6 = 1/2.
What to remember
A probability model relies on assumptions. A real die need not be fair.
Check your understanding
What is the probability of not rolling a six on a fair die?
Reveal explanation
5/6, because the five other outcomes are equally likely.