How is the cost of a plane flight related to the length of the trip? The table shows the average round-trip coach airfare paid by customers of American Airlines on each of 18 heavily traveled U.S. air routes.

a. If you want to estimate the cost of a flight based on the distance traveled, which variable is the response variable and which is the independent predictor variable?

b. Assume that there is a linear relationship between cost and distance. Calculate the least-squares regression line describing cost as a linear function of distance.

c. Plot the data points and the regression line. Does it appear that the line fits the data?

d. Use the appropriate statistical tests and measures to explain the usefulness of the regression model for predicting cost.

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Distance Route (miles) Cost Dallas-Austin Houston-Dallas Chicago-Detroit Chicago-St. Louis Chicago-Cleveland Chicago-Atlanta $125 178 232 123 238 148 262 136 301 129 593 162 New York-Miami New York-San Juan 1092 224 1608 264 New York-Chicago Chicago-Denver Dallas-Salt Lake 714 287 901 256 1005 365 New York-Dallas 1374 459 Chicago-Seattle Los Angeles-Chicago Los Angeles-Atlanta New York-Los Angeles Los Angeles-Honolulu New York-San Francisco 1736 424 1757 361 1946 309 2463 444 2556 323 2574 513