=+37. Departures 2011. What are the chances your flight will leave on time? The U.S. Bureau of Transportation Statistics of the Department of Transportation publishes information about airline performance. Here are a histogram and summary statistics for the percentage of flights departing on time each month from 1995 through September 2011.

20

# of Months 15 25 10 5

0 65 70 75 80 85 90 OT Departure (%)

n 201 y 80.752 s 4.594 There is no evidence of a trend over time. (The correlation of On Time Departure% with time is r = -0.016.)

a) Check the assumptions and conditions for inference.

b) Find a 90% confidence interval for the mean percentage of flights that depart on time.

c) Interpret this interval for a traveler planning to fly.