The line graph or X-Y chart is represented on the X-Y plane denoting trends and changing rates. Basically line charts are the best suited charts for representation of data related to time series and frequency distribution. Take a look at this chart from Microsoft as an example, which shows monthly trends in transactions. 

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Image Courtesy: microsoft

Line charts are essentially drawn out from bar graphs. If you join the upper points of the bar graph and join them, you will get a line chart only that gives us the above mentioned diagram.

Parts of a line chart or line graph

A line graph encompasses a vertical axis and a horizontal axis. 

  • Title – shows what the graph is depicting such as company sales of the year 2018, GDP of 2018-19, etc. 
  • Labels – depict what the horizontal and vertical axis are telling us. (E.g. Units sold and Total Transactions)
  • Scales – the scales denote the number or quantity of facts and data of the horizontal and vertical scales. 
  • Points – represent data on the graph through dots 
  • Lines – points are connected to form a line that represent the trend of the data (e.g., are the transactions increasing? Or Decreasing?)

Types of questions asked through a line chart

Any data that is measured against time uses a line chart. Some examples include:

  • Population of a country
  • GDP or national product 
  • Sales or profit making of a company

The questions which can be asked from this section could be of the following type:

  1. What is the trend in change of variable?
  2. What is the percentage increase or decrease in between two points of time?
  3. When was the variable parameter highest/lowest?
  4. How the does the total sales of Q1 compare to total sales of Q2? 

Some important properties of a line chart

  • You can easily detect the changing trends of the data represented by looking at the graph. 
  • While looking at the graph, specific values of the variables and how one variable is affected by another is easily seen. 
  • Line graphs are predominantly used for comparing datasets and your questions can be based on such comparisons. 
  • Slope of the graph indicates the absolute growth of the data. It does not indicate the percentage of growth. 
  • If the slope is steeper, the magnitude change is greater between those two points. 

Some important types of line charts 

  • Single variable graph 

This graph shows the changes in a single variable over a certain period of time. For example, sales of a company over 2015-2020. 

  • Continuous variable graph

For this two or more lines depict two or more dependent variables. 

  • Two scaled graph

If two variables have different units of measurements, two scales are used on the graph. 

Points to keep in mind while solving line chart questions

  • While looking at the line chart, pay attention to the details like the trends, data values, and analyse them carefully. 
  • Do not assume any information according to your own understanding, read the questions and refer only to the data given in the line chart. 
  • Most of the questions will be based on finding out averages, percentages, ratio and proportion, etc. So the formulas of all these should be on your tips. 

Some important formulas

  • Average = Sum of all values 

                   Number of values 

  • Percentages change = Final value – Initial value   x 100 

                                                     Initial value                     

  • Ratio = Comparison of like terms 

Apart from these, pay attention to the basics of mathematical aptitude while practicing questions and you will do wellt in solving line chart questions. 

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