Probability is the maths of chance. A probability is a number that tells you how likely (probable) something is to happen. Probabilities can be written as fractions, decimals or percentages.

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We often make judgements as to whether an event will take place, and use words to describe how probable that event is. For example, we might say that it is **likely** to rain tomorrow, or that it is **impossible** to find somebody who is more than \({3}~{m}\) tall.

Other commonly used words to describe the chance of an event happening include:

- certain
- very likely
- even chance
- unlikely
- very unlikely

Maths uses numbers to describe probabilities. **Probabilities can be written as fractions, decimals or percentages.** You can also use a probability scale, starting at \({0}\) (impossible) and ending at \({1}\) (certain).

Here are some events placed on the probability scale.

Have a look at ordering the probabilities in the question below.