minutes. A telephone company wants to perform a test to determine whether this average
duration of long-distance calls has changed. Twenty calls, originating from the town, were
randomly selected and the mean duration was 10.2 minutes with standard deviation of 4.8
minutes.
a) Using a 1% level of significance, test whether the mean duration of long-distance calls
from the town had increased.
[6]
b) Construct the 99% confidence interval for the population mean duration of the long-
distance calls from the town.
[4]
Fig: 1