15.19 Strong association but no correlation. Exercise 14.24 gives these data on the speed (miles per hour) and mileage (miles per gallon) of a car:
| Speed: | 25 | 35 | 45 | 55 | 65 |
| Mileage: | 20 | 24 | 26 | 24 | 20 |
The least-squares line for predicting mileage from speed is
(a) Make a scatterplot of the data and draw this line on the plot.
(b) The correlation between mileage and speed is . What does this say about the usefulness of the regression line in predicting mileage?