Refer to the Marine Technology (Jan. 1995) study of major oil spills from tankers and carriers, Exercise 2.159 (p. 120). The data for the 42 recent spills are saved in the accompanying file.

a. Construct a 90% confidence interval for the difference between the mean spillage amount of accidents caused by collision and the mean spillage amount of accidents caused by fire/explosion. Interpret the result.

b. Conduct a test of hypothesis to compare the mean spillage amount of accidents caused by grounding with the corresponding mean of accidents caused by hull failure. Use α = .05.

c. Refer to parts a and b. State any assumptions required for the inferences derived from the analyses to be valid. Are these assumptions reasonably satisfied?

d. Conduct a test of hypothesis to compare the variation in spillage amounts for accidents caused by collision and accidents caused by grounding. Use α = .02.