29. 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 thru September 2011. (www.transtats.bts.gov/HomeDrillChart.asp)

There is no evidence of a trend over time.

a) Check the assumptions and conditions for inference.

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

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

# of Months 5 10 20 20 15 n 201 y 80.752 S 4.594 65 70 75 OT Departure (%) 80 85 90