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Diagram of Data : We have seen that the collected data under investigation are the
raw materials of the statistics. If the frequency distribution and cumulative frequency
distribution table are made with them, it becomes clear to comprehend and to draw a
conclusion. If that tabulated data are presented through diagram, they become easier
to understand as well as attractive. That is why, presentation of statistical data in
tabulation and diagram is widely and frequently used method. In class VIII, different
types of diagram in the form of line graph and histogram have been discussed
elaborately and the students have been taught how to draw them. Here, how
frequency polygon, pie-chart, ogive curve drawn from frequency distribution and
cumulative frequency table will be discussed.
Frequency Polygon : In class VIII, we have learnt how to draw the histogram of
discrete data. Here how to draw frequency polygon from histogram of indiscrete data
will be put for discussion through example.
Example 3. The frequency distribution table of the weights (in kg) of 60 students of
class X of a school are is follows :

Weight (in kg) 46  50 51  55 56  60 61  65 66  70

Frequency

(No. of Students)

5 10 20 15 10

(a) Draw the histogram of frequency distribution.
(b) Draw frequency polygon of the histogram.
Solution : The class interval of the data in the table is discrete. If the class interval
are made indiscrete, the table will be :
Class interval of the weight (in
kg)

Discrete class

interval

Mid point of

class

Frequency

46  50 45 ˜ 5  50 ˜ 5 48 5

51  55 50 ˜ 5  55 ˜5 53 10

56  60 55 ˜ 5  60 ˜5 58 20

61  65 60 ˜ 5  65 ˜5 63 15

66  70 65 ˜ 5  70 ˜5 68 10

(a) Histogram has been drawn taking each square of graph paper as unit of class
interval along with x-axis and frequency along withy-axis. The class interval along
with x-axis has started from. The broken segments have been used to show the
presence of previous squares starting from from origin to 45˜5.