Common Mistakes: Data & Graphs
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Reading and creating graphs takes careful attention. Let's learn about common mistakes to avoid!
Mistake #1: Not Reading the Scale
Wrong: Assuming each line on a graph represents 1
Right: Always check the scale! A graph might count by 2s, 5s, or 10s.
Mistake #2: Forgetting the Key in Pictographs
Wrong: Counting each picture as 1 without checking the key
Right: Always read the key! Each symbol might represent 2, 5, or more items.
Mistake #3: Missing Labels
Wrong: Creating a graph without a title or axis labels
Right: Every graph needs: a title, labels for both axes, and a key if using symbols.
Practice: Find the Mistake
1. A bar graph shows sales counted by 5s. The bar reaches the 4th line. A student says sales = 4. What's wrong?
A) Nothing, 4 is correct
B) The scale counts by 5s, so it's 20
C) The answer is 5
D) You can't tell from a bar graph
Answer
B) - If counting by 5s, the 4th line = 4 x 5 = 20.
2. A pictograph shows 3 apple symbols. The key says each apple = 2 students. How many students chose apples?
A) 3 students
B) 5 students
C) 6 students
D) 2 students
Answer
C) 6 students - 3 symbols x 2 students each = 6 students.
3. A student creates a bar graph but forgets to label the y-axis. Why is this a problem?
A) It's not a problem
B) No one knows what the numbers represent
C) The bars won't show
D) The title won't fit
Answer
B) - Without labels, readers don't know what the data means.
4. When should you use a pictograph key?
A) Never
B) Only when symbols represent more than 1
C) Always when using pictographs
D) Only for bar graphs
Answer
C) - Pictographs should always have a key so readers know what each symbol represents.
5. A bar graph has bars at heights 10, 15, and 20. A student says the difference between the shortest and tallest is 2. What's wrong?
A) Nothing, 2 is correct
B) They counted bars instead of values (should be 10)
C) The answer is 15
D) You can't subtract on bar graphs
Answer
B) - The difference is 20 - 10 = 10, not the number of bars.
6. What's missing from a graph with these labels: "Favorite Colors" (title), "Blue, Red, Green" (x-axis)?
A) Nothing is missing
B) A y-axis label (like "Number of Students")
C) More colors
D) A bigger title
Answer
B) - The y-axis needs a label to explain what the numbers mean.
7. A pictograph key shows: Star = 5 votes. There are 4 stars next to "Pizza." How many votes did pizza get?
A) 4 votes
B) 5 votes
C) 9 votes
D) 20 votes
Answer
D) 20 votes - 4 stars x 5 votes each = 20 votes.
8. A graph shows data from Monday to Friday, but Thursday's bar is missing. What should you do?
A) Guess what it should be
B) Skip Thursday in calculations
C) Note that Thursday's data is missing or zero
D) Add the other days and divide by 5
Answer
C) - Missing data could mean zero or that data wasn't collected. Note it rather than guess.
9. Why is it important to start the y-axis at 0 for most bar graphs?
A) It's not important
B) So the differences between bars look accurate
C) Because graphs always start at 0
D) To save space
Answer
B) - Starting at a number other than 0 can make differences look bigger or smaller than they really are.
10. A pictograph shows half a symbol. The key says each symbol = 4. What does half a symbol represent?
A) 0
B) 1
C) 2
D) 4
Answer
C) 2 - Half of 4 = 2.
Next Steps
- Always check the scale and key before reading graphs
- Include all labels when creating your own graphs
- Continue to the Unit Quiz