Table of contents 
Bar graphs and Histograms 
Frequency Polygons 
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The science of collecting and analyzing data in large quantities, especially for inferring proportions in a whole form is known as Statistics. The word ‘statistics’ itself refers to numbers that are used to describe the relationships of data. Therefore, we can say that the field of applied mathematics that deals with data collection, organization, analysis, interpretation, and presentation is called statistics.
A Bar graph or a Histogram is the diagrammatic representation of data in statistics. In bar graphs or histograms, the use of graphs, charts, and tabular data makes it very easy to understand the concept and relationships among data.
The pictorial representation of data in groups, either in horizontal or vertical bars where the length of the bar represents the value of the data present on axis. They (bar graphs) are usually used to display or impart the information belonging to ‘categorical data’ i.e; data that fit in some category.
Reading a Bar Graph and comparing two sets of data
In order to read a Bar graph, we need to ask questions to ourselves looking at the displayed graph. Let’s understand reading a Bar graph through a very basic example,
Different types of fruits liked by People,
What does the Xaxis and Yaxis on the graph are representing?
The Xaxis represents the different types of fruits like apple, guava. while Yaxis represents the Number of people.
What is the Common base for the Bars?
The bars are showing a common base of category of fruits.
What is the scale used on the Yaxis?
The scale used is normal, i.e; 1 Unit = 1 person
Overall, what kind of information the bar graph displaying?
The bar graph is displaying the number of People liking different types of fruits.
Looking at the bar Graph, can one answer, how many people like Mango?
Yes, By observing the length of the bar, one can tell that there are 5 people who like Mango.
Noticing the graph, explain the fruit liked by most people and the fruit liked by least people?
The data displayed on the graph is easily comparable, it can be concluded that the most liked fruit is Guava and the least liked fruit is Apple.
How many more people like Guava than Mango?
There are 7 people who like guava and 5 who like Mango. Thus, we can say that there are 2 more people liking guava.
It can be concluded the following just by looking at the graph:
Properties of Bar Graph
Significance of a Bar Graph
It is always easier and more comfortable to visually understand something than to look at the large table of Numerical data. Bar graphs are extensively used in presentations and reports. It is very prominently used as it summarizes data and displays it in a frequency distribution.
Sample Problems on Bar Graph
Question 1: Draw the Bar Graph for the following table,
Solution:
Question 2: The average speed of some vehicles is shown below, Represent it through a bar graph.
Solution:
The average speed mentioned in the table is the frequency which decides the length of each bar graph, therefore, if the graph is vertical, the Average speed will be shown on the yaxis and the types of vehicles will be shown on the xaxis.
Histograms are the graphical display of data with the help of bars, the heights of the bars may vary due to different data. The similarity of a Histogram resembles a bar chart, but histogram groups numbers into different ranges. The length of each bar tells how many fall into each range, and it can be decided which ranges are to be used.
Construction and interpretation of Histogram
Difference Between Histograms and Bar graph
Sample Problems on Histogram
Question 1: In a Park, there are 28 trees of different heights, the heights can be measured in centimeters and the range of the trees lie between 100350 cms. Draw the Histogram for the following data,
Solution:
Since the height of the trees are lying between 100350, we shall start by marking the heights on xaxis in groups of 50cm each and the number of trees will be mentioned on yaxis.
Therefore, if a tree has a height of 230 cm, it will lie in the rectangle 200250.
Question 2: In the belowgiven table, the number of machines working in a factory for their fixed amount of time is shown. Draw the Histogram for the following data.
Solution:
The Histogram for the table mentioned above will have class intervals of 5 minutes on xaxis and the number of machines used should be on yaxis.
A frequency polygon is almost identical to a histogram, which is used to compare sets of data or to display a cumulative frequency distribution. It uses a line graph to represent quantitative data.
Statistics deals with the collection of data and information for a particular purpose. The tabulation of each run for each ball in cricket gives the statistics of the game. Tables, graphs, piecharts, bar graphs, histograms, polygons etc. are used to represent statistical data pictorially.
Frequency polygons are a visually substantial method of representing quantitative data and its frequencies. Let us discuss how to represent a frequency polygon.
To draw frequency polygons, first we need to draw histogram and then follow the below steps:
Let us consider an example to understand this in a better way.
Example 1: In a batch of 400 students, the height of students is given in the following table. Represent it through a frequency polygon.
Solution: Following steps are to be followed to construct a histogram from the given data:
ABCDEF represents the given data graphically in form of frequency polygon as:
Frequency polygons can also be drawn independently without drawing histograms. For this, the midpoints of the class intervals known as class marks are used to plot the points.
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