Problem-Solving and Data AnalysisHardExtrapolating along a line of best fit
Problem-Solving and Data Analysis practice question
The line of best fit for a scatterplot passes through the points (0, 8) and (10, 28). According to this line, what is the predicted value of y when x = 25?
Answer: 58
Slope: (28 − 8)/(10 − 0) = 2, and the line crosses the y-axis at 8, so y = 2x + 8. At x = 25: 2(25) + 8 = 58.
Common wrong answers
- If you answered 33
- 33 is 25 + 8, adding x to the intercept instead of multiplying x by the slope first.
- If you answered 50
- 50 is 2 × 25, the slope times x, without the y-intercept of 8.
- If you answered 70
- 70 would come from a slope of 2.8 (28/10), dividing the y-value by x instead of using the CHANGE in y over the change in x.
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