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Objective
Find the mean of a set of data
Vocabulary
Average
The sum of the data divided by the number
of pieces of data
Also called the “mean”
Vocabulary
Measure of central tendency
A number that helps describe all of the data
in a data set
Most common
Mean
Median
Mode
Vocabulary
Mean
The sum of the data divided by the number
of pieces of data
Also called the “average”
Vocabulary
Outlier
A value much higher or lower than the other
values
80, 81, 40, 77, 82
40 is the outlier
Example 1 Find Mean
Example 2 Determine How Outliers Affect Mean
READING The number of words
per sentence on one page of a
novel is shown in the table. Find
the mean.
Mean = sum of data
pieces of data
Mean = 34 + 47 +31 + 32
16
Words per Sentence
8 11
9
7
10
7
8
8
9
7
18
11
7
7
8
9
Add the data in each column
Put sum of columns in
equation
Count the number of pieces
of data and put in the
denominator
1/2
Mean = sum of data
pieces of data
Mean = 34 + 47 + 31 + 32
16
Mean =
144
16
Mean = 9
Follow order of operations
rules
P
E
MD AS
Remember fraction bar is
used as enclosures
Add the numerator
Bring down 16
Divide 144 by 16
Answer: Mean = 9 words
1/2
PRACTICE The number of days per week that members
of the middle school band practice their instrument is
shown in the table. Find the mean.
Days of Practice
6 7 5 5 3 6
5 1 4 6 7 5
Answer: Mean = 5 days per week
1/2
BASKETBALL Find the mean with and without the
outlier. Then describe how the outlier affects the mean.
Points per Game
98
102
88
76
78
44
98
101
100
77
108
86
Determine the outlier
Must find 2 means - with and without the outlier
2/2
Points per Game
mean with outlier
Mean = 276 + 223 + 294 + 263
12
98
78
100
102
44
77
88
98
108
76
101
86
Add the data in each column
Put sum of columns in
equation
Count the number of pieces
of data and put in the
denominator
2/2
Points per Game
mean with outlier
Mean = 276 + 223 + 294 + 263
12
Mean =
1056
12
Mean = 88
98
78
100
102
44
77
88
98
108
76
101
86
Follow order of operations
rules
P
E
MD AS
Add the numerator
Bring down 12
Divide 1056 by 12
2/2
mean without outlier
Mean = 276 +179 + 294 + 263
11
Points per Game
98
102
88
76
78
100
44
77
98
108
101
86
Add the data in each column
Put sum of columns in
equation
Do not add the outlier of 44
Count the number of pieces
of data and put in the
denominator (remember
don’t count the outlier)
2/2
mean without outlier
Mean = 276 +179 + 294 + 263
11
Mean =
1012
11
Mean = 92
Points per Game
98
102
88
76
78
100
44
77
98
108
101
86
Follow order of operations
rules
P
E
MD AS
Add the numerator
Bring down 11
Divide 1012 by 11
2/2
Describe how the outlier affects the mean
Mean with outlier = 88
Mean without outlier = 92
The outlier was 44 which was lower than the
other data so without the outlier the mean was
higher than with the outlier
Answer: The outlier lowered the mean by 4 points
2/2
*
EXAM SCORES Find the mean with and without the
outlier. Then describe how the outlier affects the mean.
Exam Scores
84 75 93 82
36 74 79 91
Answer: mean with outlier: 76.75; mean without outlier:
82.57;
The outlier lowers the mean of the data by about
six points.
2/2
Assignment
Lesson 2:6
Mean
9 - 18 All