Probability Basics

Probability Basics

Probability measures how likely something is, from 0 (impossible) to 1 (certain). It's often written as a fraction, decimal, or percentage.

Single events

For equally likely outcomes, the probability of an event is the number of ways it can happen, divided by the total possible outcomes. Rolling a 4 on a fair die: 1 way out of 6 outcomes = 1/6, since each face is equally likely to land face-up.

Combined events

For two independent events happening together (like two coin flips both landing heads), multiply their individual probabilities: 1/2 × 1/2 = 1/4.

Practice

What's the probability of picking a red card from a standard deck of 52?