Page 291 - Start Up Mathematics_7

data. We assume a suitable and convenient scale to decide the height of the bars along Y-axis.

In order to construct a bar graph, the following points must be kept in mind.
1. Draw two perpendicular lines and call them as horizontal and vertical axes.
2. Along the horizontal axis, mark the information given in the data like days, weeks, months,
years, subjects, places, etc. at uniform gaps.

3. Select a suitable scale to determine the heights of the bars or rectangles along the vertical
axis. For example, if 1,200 people like cricket, then 1 unit length can be taken to represent
200 people so that a bar of height 6 units can represent 1,200 people.
4. Draw bars or rectangles of equal width and height as determined in the previous point. These
bars should have uniform spacing between them. The figure so obtained is called a bar graph.

• A bar graph should always have a title.
• The horizontal and vertical axis should be labelled to show what they represent.

Example 9: The number of students Fifth Sixth Seventh Eighth Ninth Tenth
in six different classes are Class
given. Represent the data Number of 135 120 95 100 90 80
students
on a bar graph.
(a) How would you choose a scale?

(b) Which classes have the maximum and minimum number of students?
(c) Find the ratio of students of class six to the students of class eight. (NCERT)
Solution: (a) Choose a suitable scale as follows:

Start the scale at 0. The greatest value in the data is 135. So, end the scale at a
value greater than 135, say 140. Use equal divisions along the vertical axis to
choose a scale such that the length between 0 and 140 is neither too long nor
too small. Let’s take 1 unit to represent 20 students.

Y Number of students in each class
Scale: 1 unit = 20 students
140
120
Number of students 80
100

60

40
20

0 X
V VI VII VIII IX X
Classes
(b) Clearly Class V has maximum number of students and Class X has minimum
number of students.

(c) Ratio of students of class six to the students of class eight is 120 : 100, i.e.,
6 : 5.

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