Mean, median and mode
- Mean: add all the values and divide by how many there are.
- Median: the middle value when the numbers are sorted. With an even count, it is the mean of the two middle values.
- Mode: the value that appears most often. A list can have more than one mode, or none.
- Range: the largest value minus the smallest.
For 12, 15, 18, 22, 15, 30, 9: the sum is 121, so the mean is 121 ÷ 7 = 17.29. Sorted, the list is 9, 12, 15, 15, 18, 22, 30, so the median is 15. The mode is 15 and the range is 30 − 9 = 21.
Which average should I use?
The mean is affected by extreme values, so the median is better for skewed data such as incomes or house prices. The mode is useful for categories and for finding the most common value. The geometric mean suits growth rates and ratios.