30. Late arrivals. Will your flight get you to your destination on time? The U.S. Bureau of Transportation Statistics reported the percentage of flights that were late each month from 1995 through 2006. Here’s a histogram, along with some summary statistics:

We can consider these data to be a representative sample of all months. There is no evidence of a time trend.

a) Check the assumptions and conditions for inference about the mean.

b) Find a 99% confidence interval for the true percentage of flights that arrive late.

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

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# of Months 20 15 10 5 10 15 20 Late Arrival % n 144 y 20.0757 S 4.08837 25 30