Frequency Polygons

1
Frequency Polygons
A frequency distribution can be shown using a
frequency polygon.
A Frequency Polygon can be drawn onto an existing
histogram.
1. Mark the mid - points of each bar at the top
with a point.
2. Draw in straight lines connecting points.
3. Extend lines if necessary ½ a class interval
beyond first and last bars
Test Scores
20
15
Frequency
10
5
0
25-30
20-24
5-9
10-14
15-19
Marks
2
Frequency Polygons
Time Taken for Race
20
15
Frequency
10
5
0
20
50
60
10
30
40
Time in minutes
3
Frequency Polygons
Maximum Daily Temperature as Recorded by a
Gardener
20
15
Frequency
10
5
0
15
30
35
10
20
25
Temperature oC
4
Worksheet 1
Frequency Polygons
5
A frequency polygon can be drawn directly from
the frequency table by finding the mid-point of
each class interval.
Marks 5 9 10 14 15 19 20 24 25 - 30
frequency 4 10 20 13 8
Test Scores
20
15
Frequency
10
5
0
25-30
5-9
20-24
10-14
15-19
Marks
6
A frequency polygon can be drawn directly from
the frequency table by using by finding the
mid-point of each class interval.
Time 10 20 20 30 30 40 40 50 50 - 60
frequency 7 10 18 6 4
Time Taken for Race
20
15
Frequency
10
5
0
20
30
40
50
60
10
Time in minutes
7
A frequency polygon can be drawn directly from
the frequency table by using by finding the
mid-point of each class interval.
Time 10 15 15 20 20 25 25 30 30 - 35
frequency 7 15 19 6 1
Maximum Daily Temperature as Recorded by a
Gardener
20
15
Frequency
10
5
0
15
20
25
30
35
10
Temperature oC
8
Worksheet 2
9
The same 55 students sat two separate maths
tests. The scores for each are shown by the
frequency polygons below. Comment on the
differences.
It is often useful to show frequency polygons,
side by side, in order to compare distributions.
Test Scores
20
15
Frequency
10
5
0
25-30
20-24
5-9
10-14
15-19
Marks
10
A gardener recorded the maximum daily temperature
on 48 days throughout the year 2000. She repeated
this for the same dates in 2003. Comment on the
differences in temperature for these years.
Maximum Daily Temperature as Recorded by a
Gardener
20
15
Frequency
10
5
0
15
30
35
10
20
25
Temperature oC