The mean (also called the average) is one number we use to describe a whole data set. To find the mean, we use a 3-step procedure:

1. ADD all the values in the data set.
2. COUNT how many values there are. Call this number $n$.
3. DIVIDE the sum by $n$.

For example, to find the mean of $\{4, 6, 8, 6, 6\}$:

• Sum: $4 + 6 + 8 + 6 + 6 = 30$
• Count: there are $5$ values.
• Mean: $30 \div 5 = 6$.

So the mean of this data set is 6.

The procedure works the same way for decimal data sets. To find the mean of $\{2.5, 3.0, 3.5, 4.0, 2.0\}$: sum is $15.0$, count is $5$, mean is $15.0 \div 5 = 3.0$.