Will your flight get you to your destination on time? The U.S. Bureau of Transportation Statistics reported the percentage of flights that were delayed each month from 1994 through October of 2013. 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 (r = 0.07).
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.

n 238 5019.753 40-15 4.273 30 10 10 15 20 30 Delayed (96)