In statistics there are three types of average: the mean, the median and the mode. Measures of spread such as the range and the interquartile range can be used to reach statistical conclusions.

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The **mean** is the most commonly used average.

To find the mean of a list of numbers, add them all together and divide by how many numbers there are:

\[\text{mean} = \frac{\text{sum of all the numbers}}{\text{amount of numbers}}\]

The mass of 7 babies are as follows:

2.5 kg, 3.1 kg, 3.4 kg, 3.5 kg, 3.5 kg, 4 kg, 4.1 kg

Find the **mean** mass of the babies.

\(\text{mean} = \frac{2.5 + 3.1 + 3.4 + 3.5 + 3.5 + 4 + 4.1}{7} = \frac{24.1}{7} = 3.44\) (2 dp)

The mean mass of the babies is 3.44 kg.