How to find each one
- Mean: add every value, divide by the count.
- Median: sort the values. With an odd count, take the middle one; with an even count, average the two middle values.
- Mode: the value that appears most often. There can be one mode, several (bimodal, multimodal), or none if no value repeats.
- Range: largest minus smallest.
Example: 3, 7, 7, 2, 9, 4, 7, 5, 2 sorted is 2, 2, 3, 4, 5, 7, 7, 7, 9. Mean = 46 ÷ 9 ≈ 5.11, median = 5 (the 5th value), mode = 7, range = 7.
Which average should you use?
The mean uses every value, which makes it sensitive to outliers. The median depends only on order, so it resists extreme values: that is why incomes and house prices are reported as medians. The mode is the only average that works for categories (the most common eye colour). If the mean is well above the median, the data are probably skewed right; well below suggests skewed left.
Frequently asked questions
What if there are two modes?
The data are bimodal and you report both. If every value appears the same number of times, there is no mode.
How do I find the median of an even number of values?
Sort them and average the two middle values. For 4, 8, 10, 15 the median is (8 + 10) ÷ 2 = 9.
Can the mean be a number that is not in the data?
Yes, and it usually is. The mean of 1, 2, 4 is 2.33. The median of an even-sized list can also fall between data values.