In a numerical data set, what is the value called that is calculated by dividing the sum of all data items by the number of items?

The correct answer is the mean, which is a fundamental concept in statistics. The mean is calculated by adding together all the values in a data set and then dividing that sum by the total number of values. This calculation provides a measure of the central tendency of the data, representing an average value.

For example, if you have a data set consisting of the numbers 2, 3, 5, and 10, you would add these together to get 20. Since there are four numbers in this data set, you would then divide 20 by 4, resulting in a mean of 5. This process smooths out the variations in the data, providing a single value that is typical or representative of the entire set.

In contrast, the mode refers to the value that appears most frequently in a data set, while the median is the middle value when the data set is ordered from least to greatest. The range represents the difference between the highest and lowest values in the data set. Each of these measures serves a different purpose and provides distinct insights into the characteristics of the data. Therefore, the mean is specifically used to convey the average of all the values, making it the correct choice for this question.