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.

##### Solution:

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

## 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.