Frequency polygons  Graphing Data
Frequency polygons
Basic concepts:
 Frequency distribution and histograms
Lessons
Notes:
Frequency Polygons are graphs that are constructed out of a frequency table. To create a Frequency Polygon just follow these steps:
1) Create a histogram
2) Plot the midpoints for each bar on the histogram
3) Plot a point with a value of zero one bar below the smallest class. Also plot a point with a value of zero one bar above the largest class
4) Connect all the data point with a straight line

2.
Constructing a Frequency Polygon from a Frequency Distribution
The following frequency table shows the amount of time it took 45 ski racers to complete a ski course:
Lower Limit:
Upper Limit:
Frequency:
Cumulative Frequency:
80 seconds
86 seconds
3
3
86 seconds
92 seconds
5
8
92 seconds
98 seconds
12
20
98 seconds
104 seconds
8
28
104 seconds
110 seconds
16
34
110 seconds
116 seconds
11
45

3.
Interpreting a Frequency Polygon
The frequency polygon below shows the wind speed during a particular day in San Francisco Bay: