The article “Exhaust Emissions from Four-Stroke Lawn Mower Engines” (J. of the Air and Water Mgmnt. Assoc., 1997: 945–952) reported data from a study in which both a baseline gasoline mixture and a reformulated gasoline were used. Consider the following observations on age (yr) and NO_x emissions (g/kWh):                                                                                              

  

      

  

Construct scatter plots of NO_x emissions versus age. What appears to be the nature of the relationship between these two variables? [Note: The authors of the cited article commented on the relationship.]

 

Engine Age Baseline 1 2 3 4 5 2 11 7 1.72 4.38 4.06 1.26 5.31 Reformulated 1.88 5.93 5.54 2.67 6.53 Engine Age Baseline 6. 7 8 9. 10 16 12 4 .57 3.37 3.44 .74 1.24 Reformulated .74 4.94 4.89 .69 1.42