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Year 8 Interactive Maths - Second Edition

Line Graphs

A line graph is often used to represent a set of data values in which a quantity varies with time.  These graphs are useful for finding trends.  That is, finding a general pattern in data sets including temperature, sales, employment, company profit or cost over a period of time.

Example 10

A cylinder of liquid was heated.  Its temperature was recorded at ten-minute intervals as shown in the following table.

a.  Draw a line graph to represent this information.
b.  Estimate the temperature of the cylinder after 25 minutes of heating.


b.  The estimated temperature after 25 minutes of heating is 52C.

Choosing an Appropriate Graph

To choose an appropriate statistical graph, consider the set of data values.  In general, use the following guidelines:

  • Use a bar chart if you are not looking for trends (or patterns) over time; and the items (or categories) are not parts of a whole.
  • Use a pie chart if you need to compare different parts of a whole, there is no time involved and there are not too many items (or categories).
  • Use a line graph if you need to see how a quantity has changed over time.  Line graphs enable us to find trends (or patterns) over time.

Key Terms

line graph, trend

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