Mean

Description

The mean is found by adding all the values together and dividing by how many there are:

$$\text{mean} = \frac{\text{sum of values}}{\text{number of values}}$$

Example: Find the mean of 3, 7, 4, 8, 3.

$$\text{mean} = \frac{3+7+4+8+3}{5} = \frac{25}{5} = 5$$

Reverse mean questions

Sometimes you're given the mean and asked to find a missing value. The key is to work out the total first:

$$\text{total} = \text{mean} \times \text{number of values}$$

Example: The mean of five numbers is 6. Four of the numbers are 3, 8, 5, and 7. Find the fifth number.

Total must be $6 \times 5 = 30$.

The four known numbers sum to $3 + 8 + 5 + 7 = 23$.

So the fifth number is $30 - 23 = 7$.

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