In an environmental impact study for a new airport, the noise levels of various jets were measured just seconds after their wheels left the ground. the jets were either wide-bodied or narrow-bodied. the noise levels in decibels (db) are recorded here for 15 wide-bodied jets and 12 narrow-bodied jets. wide-bodied jets 109.5 107.3 105.0 117.3 105.4 113.7 121.7 109.2 108.1 106.4 104.6 110.5 110.9 111.0 112.4 narrow-bodied jets 131.4 126.8 114.1 126.9 108.2 122.0 106.9 116.3 115.5 111.6 124.5 116.2

a. do the two types of jets have different mean noise levels? report the level of significance of the test.

b. estimate the size of the difference in mean noise levels between the two types of jets using a 95% confidence interval.

c. how would you select the jets for inclusion in this study?