Bar Graphs and Dot Plots: Reading the Story

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What this lesson covers

  • Bar graphs and dot plots show how many there are of each answer.
  • In a bar graph, the taller or longer the bar, the more there are.
  • A title and labels say what the data is about.
  • Graphs help you see the story in the data.
Key idea

Bar graphs

  • Each bar is one category, like walk, car or bus.
  • The height of the bar shows how many. This is called the frequency.
  • Bars can lie on their side too. Then the length shows how many.
  • Every bar is the same width.
how 20 students in Room 5 get to school
Way to schoolStudents
Walk8
Car6
Bus4
Bike2
Key idea

Try it: build a bar graph

Key idea

Dot plots for number data

  • Draw a number line with every possible answer.
  • Put one dot above the number for each answer.
  • The tallest stack is the most common answer.
teeth lost by 12 students
Teeth lostDots
0● ●
1● ●
2● ● ● ● ●
3● ●
4●
Key idea

Try it: build a dot plot

Worked example

Describe the graph

  • Say what it shows: "This bar graph shows how 20 students in Room 5 get to school."
  • Give the frequency for each category: 8 walk, 6 come by car, 4 by bus and 2 by bike.
  • Name the most and the least: walking is the most common, biking is the least.
Worked example

Questions a graph can answer

  • Some questions need adding or subtracting.
QuestionWorkingAnswer
How many students walk or bike?8 + 210
How many more walk than take the bus?8 − 44
How many teeth did the 12 students lose in total?(2 × 1) + (5 × 2) + (2 × 3) + (1 × 4) = 2 + 10 + 6 + 422
Key idea

The story in the data

  • Most students lost 2 teeth.
  • Nobody lost more than 4.
  • Walking is the most common way to get to school. Maybe many students live close by.

Common mistakes

  • The widest bar shows the most.
    All the bars are the same width. The tallest bar shows the most.
  • A graph does not need a title.
    Give a title and labels so readers know what the graph shows.
  • The teeth lost in total is the number of dots: 12.
    12 is the number of students. Add up the teeth each one lost: 22.
  • Leave a number off the dot plot if nobody chose it.
    Keep every number on the line, even with no dots, so the gaps show.

Your turn

  • 1. Which fruit is the most popular?
  • 2. Which fruit is the least popular?
  • 3. How many students were asked?
  • 4. How many more students chose kiwifruit than apple?
  • 5. How many students chose banana or orange?
favourite fruit in Room 7
FruitStudents
Apple5
Banana7
Kiwifruit9
Orange3
1
2
3
4
5
Show answer

1. Kiwifruit 2. Orange 3. 24 (5 + 7 + 9 + 3) 4. 4 (9 − 5) 5. 10 (7 + 3)

Summary

What to take away

  • The height of a bar or a stack of dots shows how many.
  • Describe a graph with its title and the count for each category.
  • Add and subtract to answer questions about the data.
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More in Statistics

Asking Questions and Collecting DataNotesBar Graphs and Dot Plots: Reading the StoryNotes

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