Mathematicians and researchers often have large sets of data collected on a certain problem, such as the household income of American families. To summarize the data, they often use the mean, median and mode.

The mean is the average of all numbers in a data set. For example, in the data set {1,1,2,3,6,7,8}, add the total and divide by seven, the number of items in the data set. The calculation would show that the average is four.

The mode is the most commonly occurring number in a data set. In the data set {1,1,2,3,6,7,8}, the mode would be one because it appears more than any other number.

The median is the middle number in the data set. For example, given the data set {1,1,2,3,6,7,8}, the median is three because there are an equal amount of numbers greater than three and less than three.