2.12: Double Bar Graphs
Remember how Tania made a bar graph in the last Concept? Alex is going to make a double bar graph. Have you ever made a double bar graph to compare data? Which data does Alex want to compare?
Tania and Alex have kept track of how many vegetables were harvested each month. Here is their data:
July | August |
---|---|
30 carrots | 60 carrots |
10 tomatoes | 20 tomatoes |
25 zucchini | 30 zucchini |
15 squash | 25 squash |
10 potatoes | 20 potatoes |
Tania and Alex want to display their data. Alex is going to make a double bar graph to display the data from both months.
Guidance
What is a double bar graph?
A double bar graph is used to display two sets of data on the same graph. For example, if we wanted to show the number of hours that students worked in one month compared to another month, we would use a double bar graph.
The information in a double bar graph is related and compares one set of data to another.
How can we make a double bar graph?
We are going to make a double bar graph in the same way that we made a single bar graph except that instead of one bar of data there will be two bars of data. Here are the steps involved:
- Draw in the two axes. One with items we are counting and one with the scale that we are using to count.
- Decide on the best scale to use given the data.
- Draw in the bars to show the data.
- Draw one category in one color and the other category in another color.
Take a minute and copy these steps down in your notebook.
Here is the data for the number of ice cream cones sold each week at an ice cream stand during the months of July and August.
July | August | |
---|---|---|
Week 1 | 500 | 800 |
Week 2 | 800 | 900 |
Week 3 | 700 | 600 |
Week 4 | 900 | 800 |
We want to create a bar graph that compares the data for July and August. First, we will have two axes.
Next, we can write in the week numbers at the bottom and use a scale for the side. Since we have ice cream cone sales in the hundreds, it makes sense to use a scale of hundreds from 0 to 1000 counting by hundreds. Now we can draw in the bars. Let’s use blue for July and red for August.
Now let's practice. Use the bar graph to answer these questions.
Example A
What is the favorite sport of girls?
Solution: Soccer
Example B
What is the favorite sport of boys?
Solution: Basketball
Example C
Which sport is liked equally by both boys and girls?
Solution: Baseball
Now that you have learned how to make a double bar graph, let's see what the vegetable counts will look like in this data display.
To compare both months together, we organize the data in a double bar graph. The key is to use the same scale so that it is easy to compare each quantity. You can also see how the harvest amounts changed during each month. Here is the double bar graph.
This is our answer.
Vocabulary
Here are the vocabulary words in this Concept.
- Bar graph
- A way to organize data using bars and two axes. One axis represents the number of each item and the other axis represents the item that was counted.
- Double Bar Graph
- A graph that has two bars for each item counted. It still uses a scale, but is designed to compare the data collected during two different times or events. A double bar graph is a tool for comparisons.
Guided Practice
Here is one for you to try on your own.
Look at this bar graph.
What is the difference between the number of boys who chose track as their favorite sport and the number of girls who did?
Answer
To figure this out, we have to subtract. Because more girls chose track than boys, we can subtract the number of boys from the number of girls.
\begin{align*}5 - 2 = 3\end{align*}
There is a difference of 3 girls compared with boys who chose track as their favorite sport.
Video Review
Here is a video for review.
Khan Academy Reading Bar Graphs
Practice
Directions: Use the following double bar graph to answer the following questions.
1. What is this graph measuring?
2. What does the horizontal axis represent?
3. What does the vertical axis represent?
4. What is being compared?
5. Is this a single bar graph or a double bar graph?
6. What is the scale of measurement?
7. What is the interval of the scale?
8. Which planet has the greatest gravitational pull?
9. What is it's measure?
10. Which planet has the least gravitational pull?
11. What is it's measure?
12. Which planet has the greatest difference between its gravitational pull and earth's gravitational pull?
13. What is the measure of Neptune's gravitational pull?
14. What is the measure of Venus' gravitational pull?
15. Which planet has a gravitational pull that is closest to earth's gravitational pull?
Bar graph
This graph represents data in a visual way by using columns to compare quantities or amounts.Double Bar Graph
A graph that has two bars for each item counted. It still uses a scale, but is designed to compare the data collected during two different times or events. A double bar graph is a tool for comparisons.double bar graphs
Double bar graphs are two bar graphs plotted side by side.Image Attributions
Here you'll make a double bar graph to display given data.