2.21 Fuel consumption. Natural Resources Canada tests new vehicles each year and reports several variables related to fuel consumption for vehicles in different classes.¹⁰ For 2015 they provide data for 527 vehicles that use regular fuel. Two variables reported are carbon dioxide (CO₂) emissions and highway fuel consumption. CO₂ is measured in grams per kilometer (g/km) and highway fuel consumption measured in liters per 100 kilometers (L/100km).

1. (a) Make a scatterplot of the data with highway fuel consumption on the x axis and CO₂ emissions on the y axis.

2. (b) Describe the form, direction, and strength of the relationship.

3. (c) Are there any outliers or unusual observations?

4. (d) Is it useful to add a straight line to your scatterplot? Explain your answer.

5. (e) If you have access to the appropriate software, explore the use of a scatterplot smoother to understand this relationship. Summarize what you find using this method.