Speed

[Maggiekidier]

In a certain city, a man records the speeds of cars driving past his house where the speed limit sign reads 20 mph. The mean of 100 readings was 21.94 mph with a standard deviation of 3.71 mph. What speeds would be considered unusually slow in the neighborhood explain your answer?

 

[Dr.Peterson]

In your class, were you given a rule of thumb for what is considered "unusually low" or "unusually high", statistically? Perhaps a value of z?