Chapter Eight
Graphing and
Introduction to Statistics
Section 8.1
Reading Pictographs, Bar Graphs,
Histograms, and Line Graphs
Pictographs
A pictograph is a graph in which pictures
or symbols are used. This type of graph
contains a key that explains the meaning
of the symbol used. An advantage of
using a pictograph to display information
is that comparisons can easily be made.
A disadvantage of using a pictograph is
that it is often hard to tell what fractional
part of a symbol is shown.
Martin-Gay, Prealgebra, 5ed
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The pictograph shows the approximate number of
passengers traveling on the leading U.S. passenger airlines.
Leading U.S. Passenger Airlines
= 25 million passengers
Delta
United
American
Southwest
US Airways
Northwest
Source: Air Transport Association of America 1998
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Bar Graphs
Bar graphs can appear with vertical
bars or horizontal bars. An advantage
to using bar graphs is that a scale is
usually included for greater accuracy.
Martin-Gay, Prealgebra, 5ed
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Millions
Bar Graphs
28
26
24
22
20
18
16
14
12
10
8
6
4
2
0
Sao Paulo
New York City
Mexico City
Tokyo
The bar graph shows the population of the world’s largest cities.
Source: United Nations, Dept. for Economic and Social Information and Policy Analysis
Martin-Gay, Prealgebra, 5ed
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Histograms
A histogram is a special bar graph. The
width of each bar represents a range of
numbers called a class interval. The
height of each bar corresponds to how
many times a number in the class
interval occurred and is called the
class frequency. The bars in a
histogram lie side by side with no
space between them.
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40-49
1
50-59
3
60-69
2
70-79
10
80-89
12
90-99
8
14
12
Number of Students
Frequency (#
of students)
Student
Scores
Histograms
10
8
6
4
2
0
The test scores of 36
students are summarized
in the table.
40-49
50-59
60-69
70-79
Student Test Scores
80-89
90-99
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Line Graphs
Another common way to display
information graphically is by using a
line graph. An advantage of a line
graph is that it can be used to
visualize relationships between two
quantities. A line graph can also be
very useful in showing change over
time.
Martin-Gay, Prealgebra, 5ed
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Line Graphs
Tornado Deaths
30
25
20
15
10
Dec.
Nov.
Oct.
Sept.
August
July
June
May
April
March
Feb.
0
Jan.
5
Average Number of U.S. Deaths (1966-1999)
Source: Storm Prediction Center
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