How does the speed at which a car drives affect fuel economy? Owners of a taxi fleet, watching their bottom line sink beneath fuel costs, hired a research firm to tell them the optimal speed for their taxis to drive. ­Researchers drove a compact car for 200 miles at speeds ranging from 35 to 75 miles per hour. From their data, they created the model Fuel Efficiency = 32 - 0.1 Speed and created this residual plot:

a) Interpret the slope of this line in context.
b) Explain why it€™s silly to attach any meaning to the y-intercept.
c) When this model predicts high Fuel Efficiency, what can you say about those predictions?
d) What Fuel Efficiency does the model predict when the car is driven at 50 mph?
e) What was the actual Fuel Efficiency when the car was driven at 45 mph?
f) Do you think there appears to be a strong association between Speed and Fuel Efficiency? Explain.
g) Do you think this is the appropriate model for that association? Explain.

+2.0 Predicted (mpgi 25 26 27 -20