A radar unit is used to measure the speed of automoblies on an expressway during rush-hour traffic. The speeds of individuals cars are normally distributed with the mean of 62 miles per hour. If 9...

A radar unit is used to measure the speed of automoblies on an expressway during rush-hour traffic. The speeds of individuals cars are normally distributed with the mean of 62 miles per hour. If 9 percent of the cars exceeded the speed limit of 65 milies per hour, find the standard deviation of all speeds.