16Hit1600
Problem-Solving and Data AnalysisVery hardInterpreting the slope of a fitted line

Problem-Solving and Data Analysis practice question

A rental company fits the line c = 0.4m + 15 to data on the cost c, in dollars, of one-day van rentals driven m miles. Which of the following is the best interpretation of the number 0.4 in this context?

  1. A. Each additional mile driven is associated with an increase of about $0.40 in the cost of a rental.Correct
  2. B. A van driven 0 miles costs about $0.40 to rent.
  3. C. Each additional dollar of cost is associated with about 0.4 more miles.
  4. D. About 40% of the cost is due to distance driven.

Answer: A. Each additional mile driven is associated with an increase of about $0.40 in the cost of a rental.

The slope is the change in c per unit change in m: $0.40 per mile.

Why the other answers are wrong

B. A van driven 0 miles costs about $0.40 to rent.
The cost at 0 miles is the intercept, $15.
C. Each additional dollar of cost is associated with about 0.4 more miles.
This reverses the roles of the variables; the slope gives dollars per mile, not miles per dollar.
D. About 40% of the cost is due to distance driven.
0.4 is a rate, not a proportion of the total cost.

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