1. A measure of central tendency describes the center of a set of data
A measure of central tendency describes the center of a set of data. Measures of central tendency include the mean, median, and mode.
The mean is the average of the data values, or the sum of the values in the set divided by the number of values in the set.
The median the middle value when the values are in numerical order, or the mean of the two middle numbers if there are an even number of values.

2. The mode is the value or values that occur most often
The mode is the value or values that occur most often. A data set may have one mode or more than one mode. If no value occurs more often than another, we say the data set has no mode.
The range of a set of data is the difference between the least and greatest values in the set. The range describes the spread of the data.

3. Additional Example 1: Finding Mean, Median, Mode, and Range of a Data Set
The weights in pounds of six members of a basketball team are 161, 156, 150, 156, 150, and 163. Find the mean, median, mode, and range of the data set.
Write the data in numerical order.
Add all the values and divide by the number of values.
mean:
median: 150, 150, 156, 156, 161, 163
The median is 156.
There are an even number of values. Find the mean of the two middle values.

4. Additional Example 1 Continued
150, 150, 156, 156, 161, 163
modes: 150 and 156
150 and 156 both occur more often than any other value.
range: 163 – 150 = 13

5. Check It Out! Example 1
The weights in pounds of five cats are 12, 14, 12, 16, and 16. Find the mean, median, mode, and range of the data set.
12, 12, 14, 16, 16
Write the data in numerical order.
Add all the values and divide by the number of values.
median: 12, 12, 14, 16, 16
The median is 14.
There are an odd number of values. Find the middle value.

6. Check It Out! Example 1 Continued
The weights in pounds of five cats are 12, 14, 12, 16, and 16.Find the mean, median, mode, and range of the data set.
mode: 12 and 16
The data set is bi-modal as 12 and 14 both occur twice.
range: 12 – 16 = 4

7. A stem-and-leaf plot arranges data by dividing each data value into two parts. This allows you to see each data value.
The digits other than the last digit of each value are called a stem.
The last digit of a
value is called a leaf.
Key: 2|3 means 23
The key tells you how to read each value.

8. Example 2A: Reading a Stem-and-Leaf Plot
The stem-and-leaf plot below shows the numbers of defective widgets in batches of 1000 are given below. Use the stem-and-leaf plot to answer the following questions.
Number of Defective
Widgets per Batch
Stem Leaves

9. Example 2A: Reading a Stem-and-Leaf Plot
Number of Defective
Widgets per Batch
Stem Leaves
A. What is the median number of defective widgets per batch?
B. What is the mean number of defective widgets per batch?

10. Example 2A: Reading a Stem-and-Leaf Plot
Number of Defective
Widgets per Batch
Stem Leaves
C. How many orders had less than 15 defective widgets?
D. About what percent of the batches had fewer than 10 defective widgets?

11. Example 2B Reading a Stem-and-Leaf Plot
The season’s scores for the football teams going to the state championship are given in the stem-and-leaf plot below. Use the data to answer the following questions
Football State
Championship Scores
Team A Team B
3 7
2 7

12. Example 2B Reading a Stem-and-Leaf Plot
Football State
Championship Scores
Team A Team B
3 7
2 7
A. Which team had the higher median score?
B. Which team had a wider range of scores?

13. Check It Out! Example 2
The temperature in degrees Celsius for two weeks are given in the stem-and-leaf plot below. Use the data to answer the following questions.
Temperature in Degrees Celsius
Stem Leaves
0 7
1 9

14. Check It Out! Example 2
Temperature in Degrees Celsius
Stem Leaves
0 7
1 9
A. What was the range of temperatures during the two weeks?
B. What was the mean temperature during the two weeks?

15. Check It Out! Example 2
Temperature in Degrees Celsius
Stem Leaves
0 7
1 9
C. How many days had temperatures above freezing?
D. What percent of the days had temperatures in the 20’s?

16. The frequency of a data value is the number of times it occurs
The frequency of a data value is the number of times it occurs. A frequency table shows the frequency of each data value. If the data is divided into intervals, the table shows the frequency of each interval.

17. A histogram is a bar graph used to display the frequency of data divided into equal intervals. The bars must be of equal width and should touch, but not overlap.

18. Example 3: Reading a Frequency Table
The numbers of students enrolled in Western Civilization classes at a university are given on the frequency table below. Use the table to answer the following questions.
Enrollment in Western
Civilization Classes
Number Enrolled
Frequency
1 – 10 1
11 – 20 4
21 – 30 5
31 – 40 2

19. Example 3: Reading a Frequency Table
Enrollment in Western
Civilization Classes
Number Enrolled
Frequency
1 – 10 1
11 – 20 4
21 – 30 5
31 – 40 2
A. How many classes have more than 20 students?
B. If a class were selected at random, what is the probability that the class would have more than 30 students?

20. Number of Vacation Days
Check It Out! Example 3
The number of days of Maria’s last 15 vacations are shown on the frequency table below. Use the table to answer the following questions.
Number of Vacation Days
Interval
Frequency
4 – 6 5
7 – 9 4
10 – 12
13 – 15 2

21. Number of Vacation Days
Check It Out! Example 3
Number of Vacation Days
Interval
Frequency
4 – 6 5
7 – 9 4
10 – 12
13 – 15 2
A. How many more vacations lasted 4 to 6 days than lasted 13 to 15 days?
B. What percent of the vacations lasted 7 to 9 days?

22. Example 4
The histogram shows the frequencies for various enrollments in Civilizations classes. Use the histogram to answer the following questions.
A. How many classes have between 11 and 30 students?

23. Example 4
The histogram shows the frequencies for various enrollments in Civilizations classes. Use the histogram to answer the following questions.
B. If you were enrolled into a class at random, what is the probability of there being at most 10 students?

24. Check It Out! Example 4
The histogram shows the frequency for the different heights of Black Cherry Trees in an orchard. Use the histogram to answer the following questions.
A. For which range of heights are there the fewest in the orchard?
B. If a tree were selected at random, you would expect its height to be in what range?

25. Cumulative frequency shows the frequency of all data values less than or equal to a given value. You could just count the number of values, but if the data set has many values, you might lose track. Recording the data in a cumulative frequency table can help you keep track of the data values as you count.

26. Example 4: Making a Cumulative Frequency Table
The weights (in ounces) of packages of cheddar cheese are given on the table below. Use the table to answer the following questions.
Cheddar Cheese
Weight (oz)
Frequency
Cumulative
18-20 6
21-23 2 8
24-26 5 13
27-29 3 16

27. Example 5: Reading a Cumulative Frequency Table
Cheddar Cheese
Weight (oz)
Frequency
Cumulative
18-20 6
21-23 2 8
24-26 5 13
27-29 3 16
A. How many packages weighed less than 24 ounces?
B. What percent of packages weighed less than 27 ounces?

28. Vowels in Sentences 28-31 2 32-35 ___ 9 36-39 5 40-43 3
Check It Out! Example 5
The number of vowels in each sentence of a short essay are shown on the cumulative frequency table below. Fill in the missing values.
Vowels in Sentences
Number
Frequency
Cumulative
28-31 2
32-35
___ 9
36-39 5
40-43 3