A **probability** is the *chance* of something happening.

Probabilities are measured on a **Probability Scale**. The scale starts at 0 and goes up to, and includes, 1. Probabilities can be given either as a fraction or as a decimal, but can never be less than 0 or greater than 1.

A probability of 0 means that the chance of an **event** happening is **impossible**. At the other end of the scale, a probability of 1 means that it is **certain** to happen.

Some terms used in probability have specific meanings:

**Random** is an event that is not influenced by other events,and whose result cannot be determined in advance;

**Fair** is an event that cannot be influenced by other factors;

**Bias** is an event that can be influenced by other factors, and includes items such as a weighted die which influences the outcome of any throw.

There are two types of probability: **Theoretical Probability** is the chance of something happening in an ideal world. For example, determining the probability of obtaining a 6 by throwing a fair die, without actually throwing it.

**Experimental Probability** is the result of carrying out an experiment. For example, throwing a die 100 times, in order to determine whether the die is biased.

Which event is more likely to happen, an event with a probability of 0.3, or an event with a probability of 0.7?

The second event, as it is a higher value on the probability scale.

Answer: 0.7

Jon says that there is a probability of 10, on a scale of 1 to 10, that there will be a test next week. What is wrong with his statement?

The probability scale runs from 0 to 1 (inclusive).

Answer: Probabilities must not be greater than 1.

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