Double bar graphs
Double bar graphs, also called double bar charts, help us to compare or present more than one kind of information, situations, or events instead of just one by using bars.
What you see above is a double bar chart. Take a close look at it and study it carefully, so you can become familiar with its features.
After you have examined the double bar chart above, here are a few good observations you can make from the graph:
 The scale is on the left of the graph and it is 10 units.
 The title is "Scores on a Fractions Test with or without Preparation"
 Preparation helped students to score higher on the fractions test.
 The lowest score without preparation is 45 and the highest score without preparation is 85.
 The lowest score with preparation is 55 and the highest score with preparation is 100.
 The students who made the most improvement are Darline, Carla, and John. Their score improved by 15.
 The student who made the least improvement is Peter. Although Jetser's score is still slow, he improved by 10 points while Peter's score improved only by 5 points.
How to construct double bar graphs
1. Decide what title you will give the graph
2. Decide if you want horizontal or vertical bars
3. Choose a scale
4. Put label on the axes
5. Draw the bars
Example
Using the table shown below, let us construct a double bar chart. We will follow all steps outlined above in order to construct the double bar graph.
1. The title can be clearly seen from the table. It is scores on a practice test (pretest) and a test.
2. We will choose vertical bars.
3. Since the scores differ from one another mostly by 5, 10, 15, or 20, it make sense to chose a scale of 10.
If the variation between scores were like 1, 2, 3, 4, or 5, it would have been better to choose a scale of 1 or 2.
4. We can put the names of the students on the x axis and the scores on the y axis. If we had decided to make horizontal bars, we would have put the names of the students on the y axis and the scores on the x axis.
5. Finally, we draw bars. The double bar graph is shown below:

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