Problem-Solving and Data AnalysisMediumPrediction from a line of best fit
Problem-Solving and Data Analysis practice question
For a group of students, the line of best fit relating hours of television watched per week, x, to score on a quiz, y, is y = −0.4x + 30. What score does the model predict for a student who watches 10 hours of television per week?
Answer: 26
Substitute x = 10: y = −0.4(10) + 30 = −4 + 30 = 26.
Common wrong answers
- If you answered 4
- 4 is 0.4 × 10 alone. The model adds the intercept, 30, and the slope term is negative: 30 − 4.
- If you answered 30
- 30 is the predicted score at x = 0, the intercept. At 10 hours the score drops by 4.
- If you answered 34
- 34 is 30 + 4 — the slope is negative, so 0.4(10) = 4 is subtracted from 30, not added.
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