Arithmetic mean (average)
The sum of a set of numbers divided by how many there are.
The arithmetic mean, commonly called the average, is the sum of all values divided by the count of values. It's the most familiar measure of central tendency, but it is sensitive to outliers — a single very large or small value can pull it far from where most data sits. When outliers or skew are a concern, the median is often a more representative summary.
Example: The mean of 10, 20, 30, 40 is (10+20+30+40) ÷ 4 = 25.