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 NOx emissions (g/kWh):

Engine 12345 Age 0 0 2 11 7 Baseline 1.72 4.38 4.06 1.26 5.31 Reformulated 1.88 5.93 5.54 2.67 6.53 Engine 6 7 8 9 10 Age 16 9 0 12 4 Baseline .57 3.37 3.44 .74 1.24 Reformulated .74 4.94 4.89 .69 1.42 Construct a scatter plot. Does there appear to be a very strong relationship between the two types of concentration measurements? Do the two methods appear to be measuring roughly the same quantity? Explain your reasoning. 4.

A study to assess the capability of subsurface flow wetland systems to remove biochemical oxygen demand (BOD) and various other chemical constituents resulted in the accompanying data on mass loading (kg/ha/d) and mass removal (kg/ha/d) (“Subsurface Flow Wetlands—A Performance Evaluation,” Water Envir. Res., 1995: 244–247).

x 5 BOD y 5 BOD x 3 8 10 11 13 16 27 30 35 37 38 44 103 142 y 4 7 8 8 10 11 16 26 21 9 31 30 75 90

a. Construct boxplots of both mass loading and mass removal, and comment on any interesting features.

b. Construct a scatter plot of the data, and comment on any interesting features.

x 47 62 65 70 70 78 95 100 114 118 y 38 62 53 67 84 79 93 106 117 116 x 124 127 140 140 140 150 152 164 198 221 y 127 114 134 139 142 170 149 154 200 215 Construct scatter plots of NOx 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.]