Use the Empirical Rule. The mean speed of a sample of vehicles along a stretch of highway is 68 miles per hour, with a standard deviation of 5 miles per hour. Estimate the percent of vehicles whose speeds are between 53 miles per hour and 83 miles per hour. (Assume the data set has a bell-shaped distribution.) . . . Approximately|% of vehicles travel between 53 miles per hour and 83 miles per hour