The four measures of center are mean, median, mode, and midrange. Mean – The mean is what you know as the average. It is calculated by taking all of the values in a set and dividing them by the total number of values in that set. The mean is very sensitive to outliers (more on outliers in a little bit).
Rules to find the best measure to describe data. If the data points do not repeat and if there are no extreme values the best measure of center to describe a data set is mean. If some of the data points repeat, the one that has maximum occurrence is the mode, which is the best measure of center in this case for the data set.