Arrivals 2011. Will your flight get you to your destination on time? The U.S. Bureau of Transportation Statistics publishes information about airline performance. Here is the summary statistics for the percentage of flights departing on time each month from 1995 through September of 2011.
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. Find 90% confidence interval for the true percentage of flights that depart on time