Cogito
Grade 8 Math · Chapter 10 · Lesson 3
Two-Way Tables
Two categories at once.
10 problems · about 19 minutes · 8.SP.A.4
What this lesson teaches
The child reads a two-way table and uses relative frequencies to judge an association.
- A two-way table sorts data by two categories at once.
- Rows, columns, and the grand total must all agree.
- Compare proportions rather than counts, because groups differ in size.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — The Line of Best Fit: y = 5x + 2. What is y at x = 3?
Answer 17
Why 17.
Review — Scatter Plots and Association: Fitted line y = 2x + 3. Predict for x = 6.
Answer 15
Why 15.
Review — Volume of Cones, Cylinders, and Spheres: A cylinder holds 210. Its matching cone holds?
Answer 70
Why 70.
Warm Up
Straightforward practice. Get the method working first.
3 problems18 out of 24. What percent?
Answer 75
Why 75%.
A row has 7 and 13. Row total?
Answer 20
Why 7 + 13.
20 out of 50. What percent?
Answer 40
Why 20 ÷ 50.
Build It Up
The same ideas with more to keep track of.
2 problemsShould counts be compared directly across differently sized groups? 1 for yes, 0 for no.
Answer 0
Why Bigger groups give bigger counts.
9 out of 12. What percent?
Answer 75
Why Three quarters.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Row Total: A row has 12 and 18. What is the row total?
Answer 30
Why 30.
The Proportion: 15 out of 60. What percent is that?
Answer 25
Why 25%.