Topic: Graphs

Subtopic: Bar Graphs

Grades: 3-5

Inez and her grandmother are having an argument. Inez’s grandmother says Inez is spending too much time talking on the telephone each week. But Inez says she’s not spending much more time talking on the phone than she is doing chores or having free time. In this activity, your students learn how choosing the right scale for a bar graph can help make a persuasive argument.

Learning Objective: Students make and use bar graphs to picture information and to persuade.

NCTM Standard: Representation

DIRECTIONS

Materials Needed:

- Graph paper

- Copies of Worksheet 1 and Worksheet 2 (see below)

Class Periods: 1

1. On separate sheets of graph paper, draw and label the horizontal and vertical axes of two graphs as follows:

Worksheet 1

[Graph Title:] Read My Bar Graph

Horizontal Axis (Activity): FREE TIME CHORES PHONE

Vertical Axis (Hours): 0, 2, 4, 6, 8, 10, 12

Worksheet 2

[Graph Title:] Read My Bar Graph

Horizontal Axis (Activity): FREE TIME CHORES PHONE

Vertical Axis (Hours): 0, 10, 20, 30, 40, 50, 60

Have students work in two groups. Each group will need a copy of both Worksheets 1 and 2.

2. Share the story in the introduction and the numbers below with your class.

How Inez Spends Her Time

Activity Hours per week

Free time 3

Doing chores 5

Talking on the phone 10

3. Give each group copies of the “Read My Bar Graph” worksheets.

4. Tell one group to make a bar graph to argue for Inez that she doesn’t spend too much time on the phone. Which graph and scale will be more persuasive for this argument? (The graph with the 10-hour scale.) Tell the other group to make a bar graph to argue for Inez’s grandmother that Inez spends too much time on the phone compared to other activities. Which graph will be better for this argument? (The graph with the 2-hour scale.) Have groups re-label their graphs either “Inez’s Graph” or “Grandma’s Graph.”

5. Post both bar graphs on the board. Discuss how the graphs are the same and different. (The graphs have the same data, but different scales. Because Inez’s Graph uses a bigger scale, the bars look almost the same height. Because Grandma’s Graph uses a smaller scale, the bars show more differentiation.)

Cyberchase Episode: Raising the Bar

The main Cybrary is under attack. Hacker, disguised as an exterminator called the Vermin Vexer, has released a mysterious cyberbug that is systematically destroying certain information — but Ms. Fileshare, the overworked Cybrarian, is too busy to notice. When Hacker uses bar graphs to confuse Ms. Fileshare, the kids create bar graphs of their own to counter his contentions. Which graph will Ms. Fileshare believe? And what information is Hacker trying to destroy?

The Big Idea:
Represent numbers of different things in a bar graph and you can compare values at a glance, communicate with others and even persuade them.

Cyberchase FOR REAL (Epilogue)

“When Harry Met Bianca”: In their new jobs at a movie theater, Harry and Bianca compete to sell the most snacks at the concession stand. At first a comparison of bar graphs charting their sales suggests Harry has sold the most. However, when Bianca points out that the use of different scales on the graphs is misleading, she discovers that they both have sold the same amount, and both are worthy of the cherished title “Employee of the Month.”

Online games featuring similar math themes:
Bugs in the System (The player has to clear a room of bugs by clicking and dragging them onto a graph.)