Cogito
Grade 8 Math · Chapter 10 · Lesson 1
Scatter Plots and Association
Two measurements from the same thing.
10 problems · about 19 minutes · 8.SP.A.1, 8.SP.A.2, 8.SP.A.3
What this lesson teaches
The child reads a scatter plot, describes association, and fits a line informally.
- A scatter plot shows two measurements from each thing.
- Rising to the right is positive association, falling is negative.
- A fitted line predicts, but association is not cause.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Volume of Cones, Cylinders, and Spheres: A cylinder holds 210. Its matching cone holds?
Answer 70
Why 70.
Review — Distance Between Two Points: From (0, 0) to (8, 15). Distance?
Answer 17
Why 17.
Warm Up
Straightforward practice. Get the method working first.
4 problemsFitted line y = 2x + 3. Predict for x = 6.
Answer 15
Why 15.
What does a negative association look like?
Answer The points fall to the right.
Why Falling to the right.
Points rise to the right. Positive or negative?
Answer Positive.
Why Both increase together.
Fitted line y = 3x + 2. Predict for x = 5.
Answer 17
Why 15 + 2.
Build It Up
The same ideas with more to keep track of.
2 problemsFitted line y = x + 4. Predict for x = 6.
Answer 10
Why 6 + 4.
Does association prove cause?
Answer No.
Why Rising together is not enough.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Direction: Points fall to the right. What kind of association is that?
Answer Negative.
Why Negative association.
The Prediction: A fitted line is y = 2x + 1. What does it predict when x = 4?
Answer 9
Why 9.