Grade 8 · Math · Unit 10 of 18
Scatter Plots & Stories
Two-variable data and misleading graphs
What your child practises
Deciding when two-variable data is needed, picking the best graph, describing scatter plots as strong, weak, positive, negative or none, spotting outliers, and noticing graphs that mislead.
Ontario Curriculum expectation: D1.1–D1.6 · one- and two-variable data, choosing graphs, scatter plots, strong and weak relationships, outliers and misleading graphs
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
On a scatter plot, as the x-values increase, the y-values go down. The points are loosely scattered around a line. How would you describe the relationship?
- strong negative
- weak negative
- weak positive
- strong positive
Show answer
weak negative
Hint: Positive means both go up together; negative means one goes up as the other goes down. Strong means the points are close to a line.
Question 2
A student collects data on hours of practice and number of free throws made. Which graph best shows whether the two are related?
- a pictograph
- a bar graph with one bar
- a scatter plot
- a circle graph
Show answer
a scatter plot
Hint: Two numerical variables measured for each person fit a scatter plot.
Question 3
The points on a scatter plot are spread out with no pattern. How would you describe the relationship?
- strong positive
- none
- strong negative
- weak positive
Show answer
none
Hint: If one variable does not predict the other, there is no relationship.
Question 4
All of the points but one lie on a line. Which point is the outlier?
Points on a scatter plot x y 1 10 2 14 3 18 4 35 5 26 6 30 - (4, 35)
- (2, 14)
- (1, 10)
- (3, 18)
Show answer
(4, 35)
Hint: An outlier does not fit the pattern of the other points. Find the point that is far from the line the others make.
Question 5
Every graph should show…
- the largest values at the left
- a title, labelled axes, a suitable scale and a source
- only the data points
- the most colourful design
Show answer
a title, labelled axes, a suitable scale and a source
Hint: These features let readers understand and trust the graph.
Question 6
A graph has no title and no labels on its axes. What is the problem?
- Nothing, because the shape tells the story.
- Readers cannot tell what the data shows.
- The data must be wrong.
- The graph must be a scatter plot.
Show answer
Readers cannot tell what the data shows.
Hint: A good graph has a title, labels, units and a source.