Using Measures of Central Tendency
Lesson Preview
What You'll Learn
- To find mean, median, and mode
- To make and use stem-and-leaf plots
… And Why
To analyze real-world employment data, as in Example 1
Finding Mean, Median, and Mode
To understand a set of data, you need to organize and summarize the data using a measure of central tendency. Mean, median, and mode are all measures of central tendency.
You must decide which measure of central tendency best describes a set of data. Below is a review of mean, median, and mode, and where you would use each as the measure of central tendency.
Key Concepts
Review Mean, Median, Mode
mean = 
Use the mean to describe the middle of a set of data that does not have an outlier. An outlier is a data value that is much higher or lower than the other data values in the set. The mean is often referred to as the average.
The median is the middle value in the set when the numbers are arranged in order. For a set containing an even number of data items, the median is the mean of the two middle data values.
Use the median to describe the middle of a set of data that does have an outlier.
The mode is the data item that occurs the most times. It is possible for a set of data to have no mode, one mode, or more than one mode.
Use the mode when the data are nonnumeric or when choosing the most popular item.
Real-World 
Connection
WagesFind the mean, median, and mode of the data in the line plot below. Which measure of central tendency best describes the data?
Students often ask, "What grade do I need on the next test to bring up my average?" The example below shows you how to solve that kind of problem.
Solving an Equation
Suppose your grades on three history exams are 80, 93, and 91. What grade do you need on your next exam to have a 90 average on the four exams?
The range of a set of data is the difference between the greatest and least data values. The range gives you a measure of the spread of the data.
Finding the Range and Mean of Data
Find the range and mean of each set of data. Use the range to compare the spread of the two sets of data.
Interactivity Use the Interactivity to explore four different ways to describe a set of data: the mean, the median, the mode, and the range.
