Question: Flight Time – A researcher for the FAA wants to estimate the average flight time (in minutes) from Albuquerque, New Mexico to Dallas, Texas for flights with American Airlines. He randomly selects nine flights between two cities and obtains the data shown. Assume that σ = 8 minutes.

117 95 109 103 111 91 100 99 106

a. Use the data to compute a point estimate for the population mean flight time between Albuquerque and Dallas on an American Airlines flight.

b. Because the sample size is small, we must verify that flight time is approximately normally distributed and the sample does not contain any outliers. The normal probability plot and boxplot are shown next. Are the conditions for constructing a Z-interval satisfied?

90 100 110 120 Flight Time

(c) Construct a 95% confidence interval for the flight time. Interpret this interval.

(d) Construct a 90% confidence interval for the flight time. Interpret this interval.

(e) What happened to the width of the interval when the level of confidence decreased?

Explain why this result is reasonable.