Use the Empirical Rule. The mean speed of a sample of vehicles along a stretch of highway is 64 miles per hour, with a standard deviation of 3 miles per hour. Estimate the percent of vehicles whose speeds are between 58 miles per hour and 70 miles per hour. (Assume the data set has a bell-shaped distribution.) . . . Approximately |% of vehicles travel between 58 miles per hour and 70 miles per hour