# Key Ideas of Probability

## Key Terms

When we are looking at mathematical probability we have several key terms.

**Event**: An event is something that happens that is recorded. For example throwing a coin is an event.

**Outcome**: An outcome is the result of an event.

**Theoretical probability**: This is the probability that something will happen in theory, it is based on the assumption that is something is tried an infinite number of times the outcomes will be this way.

**Experimental probability**: This is the probability calculated from an experiment

**Certain**: Something that will definitely happen.

**Impossible**: Something that in no way can happen

**Even chance**: Something that has a 50% chance of happening and a 50% chance of not happening.

**Mutually exclusive**: an event that has two or more outcomes that cannot be true at the same time. For example when you throw a coin you can only get one outcome, a head or a tail, it’s not possible to get both outcomes simultaneously.

**Bias**: Favouritism or when something has an unfair advantage, when the probability of each event is not equal there will be bias.

**Relative Frequency**: The probability of something relative to a number of trials or an experiment that has happened.

## The probability scale with words and numbers

Probabilities can be a decimal, a fraction, a percentage and they can also sometimes be written as words.

Below is the probability scale that you need to know!

It’s impossible for a dinosaur to go for tea with the queen.

It’s unlikely that you’ll win the lottery!

There’s an even chance of throwing a tail!

It’s likely that you’ll pass!

It’s certain that there will be a Monday next week.

- How could you describe in numerical terms an event that is certain to happen?
- Your answer should include: 1 / 100 / 100%
- I throw a coin, what is the probability of throwing a tail?
- Your answer should include: Even / 0.5 / 50 / 50% / 1/2