Class 8 Notes - Introduction to Graphs

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Introduction to Graphs

Graphs are visual representations of data. They help us understand and analyze information quickly and easily. In mathematics, graphs are used to show relationships between quantities, trends, and patterns.

Why Use Graphs?

  • To organize and display data clearly
  • To compare different sets of data
  • To identify trends and patterns
  • To make predictions based on data

Types of Graphs

  • Bar Graph: Uses bars of equal width to represent data. The length of each bar shows the value.
  • Histogram: Similar to a bar graph but used for continuous data divided into intervals.
  • Line Graph: Uses points connected by lines to show changes over time.
  • Pictograph: Uses pictures or symbols to represent data.
  • Pie Chart (Circle Graph): Shows data as parts of a whole using sectors of a circle.

Reading a Graph

  • Look at the title to understand what the graph is about.
  • Check the axes (horizontal and vertical) to see what is being measured.
  • Read the scale to interpret the values correctly.
  • Observe the labels for each axis and data point.

Drawing a Bar Graph: Steps

  1. Draw two perpendicular lines (axes). Label the horizontal axis (x-axis) and vertical axis (y-axis).
  2. Mark equal intervals on the y-axis according to the scale.
  3. Write the categories or items on the x-axis.
  4. Draw bars for each category up to the correct value on the y-axis.
  5. Give your graph a title.

Example: Bar Graph

The following table shows the number of books read by students in a week:

Student Number of Books
Alice 4
Bob 6
Charlie 3
Diana 5

To draw a bar graph, mark the students on the x-axis and the number of books on the y-axis. Draw bars up to the correct number for each student.

Uses of Graphs in Daily Life

  • Weather charts
  • Population statistics
  • Sports scores
  • Business sales data
  • School attendance records

Practice Questions

  1. What is a bar graph? How is it different from a line graph?
  2. Draw a bar graph for the following data: Apples sold on Monday – 10, Tuesday – 15, Wednesday – 7, Thursday – 12, Friday – 9.
  3. Why is it important to label the axes and give a title to your graph?
  4. Give two examples of where you see graphs in newspapers or TV.

Summary

  • Graphs help us represent and understand data visually.
  • Common types include bar graphs, line graphs, histograms, pictographs, and pie charts.
  • Always label axes and give your graph a title.
  • Graphs are useful in many real-life situations.