Problem-Solving and Data AnalysisMediumPredicted increase over an interval
Problem-Solving and Data Analysis practice question
A line of best fit for a set of data relating a car's speed x, in kilometres per hour, to its stopping distance y, in metres, is y = 1.5x + 20. According to the line, by how many metres does the predicted stopping distance increase when the speed rises from 40 to 60 kilometres per hour?
Answer: 30
The slope 1.5 is the increase per km/h. A rise of 20 km/h gives 1.5 × 20 = 30 metres. (Check: 80 at 40, 110 at 60.)
Common wrong answers
- If you answered 20
- 20 is the y-intercept — the predicted distance at speed 0 — not the change.
- If you answered 80
- 80 is the predicted distance at 40 km/h.
- If you answered 110
- 110 is the predicted distance AT 60 km/h, not the increase.
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