CBSE Notes Class 9 Maths Chapter 12 Statistics

1.0Introduction to Statistics

It is one of the branches of maths that deals with collecting, analysing, presenting, and interpreting data. Statistics makes large amounts of data meaningful by summarising and appropriately presenting them. To do this, we use visual representation methods of these data in the form of graphs of different kinds. 

2.0CBSE Class 9 Maths Chapter 12 Statistics - Revision Notes

What is Graphical Representation of Data?

It is well-versed that one picture is better than a thousand words. By doing the graphic representation of data, we do the same. Usually, comparisons among the individual items are best shown with the help of Graphs. It is easy to understand data with the help of a graph. There are different types of graphs used to show different types of data.

Steps for Drawing a Graph

• Draw a horizontal axis along the x-axis and label it with categories such as subjects, colours, and so on.
• Draw a vertical axis along the y-axis and label it with the frequencies or values, such as the number of students or sales.
• Decide on an appropriate scale for the y-axis; for instance, 1 unit = 5 students.
• For each entry on the x-axis, draw a bar such that its height is the same as the frequency or value on the y-axis.
• Place a label on every bar or write it at the top of every bar.

1. Bar Graphs 

A bar graph presents the data in the form of rectangular bars. In this, the lengths or heights of the bars are proportional to the values or frequencies of various categories. It can be used to compare the groups. Let’s understand the bar graph with an example.

Example: The following table shows the number of books read by students of a class. Draw a bar graph for the following and answer the questions below. 

Q1: How many students read more than 6 books? 

Answer: 16

Q2: How many students read 8 or less than 8 books? 

Answer: 35

2. Histograms 

A histogram is a graphical representation of the spread of numerical data. It is a chart to represent the frequency or count of observations in certain ranges or intervals using adjacent bars - as opposed to a bar graph where the bars are not adjacent. The height of every bar indicates the amount of data that lies within that given interval. For example: 

Example: The data given below show the marks scored by students in the Class 9th Maths test.

Draw a histogram based on the given data and find No. Of Students who failed the examination. (A score below 30 fails). 

Answer: 5 Students failed the maths test in class 9th.

3. Frequency Polygon

A “frequency polygon” is a line graph that indicates the frequency of certain values that appear in a dataset. You make one by joining the middle points of the tops of histogram bars with straight lines, increasing the pattern in data to be clearer to discern.

Class Mark is used to find the midpoints of each frequency to label the graph. The formula for class Mark is as follows: 

$ClassMark=\frac{\text{ Upper Limit }+\text{ Lower Limit }}{2}$

For Example, The Data Given Below shows the Cost of Living (In hundreds) by week. 

Draw a frequency Polygon for the following Data. 

Besides making a Histogram, you can also make only lines to show the frequency polygon. Like this: 

3.0Key features of CBSE Maths Notes Class 9 of Chapter 12

• The notes provide a step-by-step guide along with solved problems for easy understanding of how to solve questions. 
• The notes have been updated with the latest CBSE pattern and syllabus. 
• These notes are written in easy-to-understand language; hence, they are ideal for self-learning. 
• Accuracy is ensured throughout the notes for learning without any hindrance.