Question

what is the main purpose of a double bar graph?
to display changes over time
to show the parts of a whole
to compare two sets of data side by side
to show the relationship between 4 or more variables

Explanation:

A double - bar graph is used to visually compare two sets of data side - by - side. Line graphs are better for showing changes over time, pie charts for showing parts of a whole, and scatter plots or other more complex graphs for relationships between 4 or more variables.

Answer:

To compare two sets of data side by side