This Question: 2 pts 31 of 36 (32 complete) Use the Empirical Rule. The mean speed of a sample of vehicles along a stretch of highway is 69 miles per hour, with a standard deviation of 3 miles per hour. Estimate the percent of vehicles whose speeds are between 60 mile a bell-shaped distribution.) Approximately % of vehicles travel between 60 miles per hour and 78 miles per hour