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.

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.

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25 10 65 70 85 90 OT Departure (%) n 201 у 80.752 5 4.594 3