In an environmental impact study for a new airport, the noise level of various jets was...

In an environmental impact study for a new airport, the noise level of various jets was 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.

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 level between the two types of jets using a 95% confidence interval.

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