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.