The municipal government will install new parking meters in various parts of the city which will charge $1.50 for every 30 minutes. Parking meters are not very popular as it is, so the mayor wants to limit bad publicity and demands that a parking meter will raise a violation alarm before the 30 minutes are up only 2.5% of the time. He also wants to limit lack of revenues and that therefore the average time until a violation occurs will be 30.5 minutes. Assuming that the Normal model applies, what must be the standard deviation of a new parking meter?