Pesticides applied to an extensively grown crop can result in inadvertent areawide air contamination. Environmental Science & Technology (Oct. 1993) reported on air deposition residues of the insecticide diazinon used on dormant orchards in the San Joaquin Valley, California. Ambient air samples were collected and analyzed at an orchard site for each of 11 days during the most intensive period of spraying. The levels of diazinon residue (in mg/m³) during the day and at night are recorded in the table. The researchers want to know whether the mean diazinon residue levels differ from day to night.

a. Analyze the data using a 90% confidence interval.
b. What assumptions are necessary for the validity of the interval estimation procedure of part a?
c. Use the interval, part a, to answer the researchers’ question.

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DIAZINON Diazinon Residue Date Day Night Jan. 11 5.4 24.3 12 2.7 16.5 13 34.2 47.2 14 19.9 12.4 15 2.4 24.0 16 7.0 21.6 17 6.1 104.3 18 7.7 96.9 19 18.4 105.3 20 27.1 78.7 21 16.9 44.6