The Bureau of Transportation Statistics releases information concerning the monthly percentage of U.S. airline flights that land no later than 15 minutes after scheduled arrival. The average of these percentages for the 12 months in 2010 was 78.5%. These data become available as soon as feasible. However, the airlines can provide preliminary results by obtaining a sample. The file titled Ontime contains the sample data indicating the number of minutes after scheduled arrival time that the aircraft arrived. Note that a negative entry indicates the minutes earlier than the scheduled arrival time that the aircraft arrived.
a. Calculate the proportion of sampled airline flights that landed within 15 minutes of scheduled arrival.
b. Calculate the probability that a sample proportion of on-time flights would be within ± 0.06 of a population proportion equal to 0.785.
c. If the airlines’ goal was to attain the same proportion of on-time arrivals as in 2010, do the preliminary results indicate that they have met this goal? Support your assertions.