The mean describes an entire sample with a single number that represents the center of the data. The mean is the arithmetic average. You calculate the mean by adding up all of the observations and then dividing the total by the number of observations.
For example, if the weights of five apples are 5, 5, 6, 7, and 8, the average apple weight is 6.4.
5 + 7 + 6 + 5 +9 / 5 = 6.4
The mean is sensitive to skewed data and extreme values. For data sets with these properties, the mean gets pulled away from the center of the data. In these cases, the mean can be misleading because the most common values in the distribution might not be near the mean.