It would seem that you are only concerned with packages that would take longer than normal time to delivered. "Beyond" could infer either direction.
95% = mean + 1.645 SD
Insert value and solve.
If it were either direction:
95% = mean ± 1.96 SD
Express Courier Service has found that the delivery time for packages is normally distributed with mean 14 hours and standard deviation 2 hours. What should be the guaranteed delivery time on all packages in order to be 95% sure that the package will be delivered before this time? (Hint: note that 5% of the packages will be delivered at a time beyond the guarantee time period)
1 answer
1 answer