Probability — the basics

A probability is a number between 0 and 1 that expresses how strongly we believe something will happen.

Event

A possible outcome ("it rains tomorrow").

Probability P(A)

How likely event A is. P(rain) = 0.3 = 30 %.

Independent events

One doesn’t affect the other. Coin flips.

Distribution

A map from every event to its probability.

A simple distribution

Heights show the probability of each outcome.