Question: 9

The times taken by buses to travel between two stops on a route follow a normal pattern of variation with a mean of 13.9 minutes. A commuter makes this journey ten times each week. One week she times the ten journey and works out that the standard deviation of them is 1.7 minutes. Treating the ten journeys in a week as a random sampling:

A) What mean journey time will be exceeded one week in twenty?

B) What mean journey time will be exceeded one week in forty?

C) What mean journey time will not be exceeded 90% of the time?