Probability

Ever wondered if it'll rain tomorrow or if you'll win a game? That's probability! It's a math way to guess how likely things are to happen.

An outcome is one possible result of a random experiment.

All possible outcomes are the complete list of everything that could happen in a random experiment.

What are all the possible outcomes when you flip a coin?

What are all the possible outcomes when you roll a six-sided die?

An event is a set of outcomes from all possible outcomes.

In the experiment of rolling a die, find the outcomes that correspond to rolling a number greater than 4.

We often use words to talk about probability. If something will never happen, it's impossible. If it will definitely happen, it's certain. In between, we say things like 'likely,' '50-50 chance,' or 'unlikely.' We can line them up from least to most likely.

• Impossible: It can’t happen.
  Example: Riding a dinosaur.
• Less likely: It probably won’t happen.
  Example: Rolling a die and getting a 3.
• Even chance: It has the same chance to happen or not.
  Example: Tossing a coin and getting head.
• Most likely: It will probably happen.
  Example: Smiling at school today.
• Certain: It will happen.
  Example: The sun will rise tomorrow.

When you flip a coin, there are two possible outcomes: heads or tails. The chance of getting heads is the same as getting tails—it’s 1 out of 2! In math, we write:
This means heads will happen about half the time!

The probability of an event, written \(P(\text{event})\), is a number that tells us how likely the event is to happen. It's always between 0 (impossible) and 1 (certain).