About 68%
Given : The mean speed of a sample of vehicles along a stretch of highway is 66 miles per hour, with a standard deviation of 4 miles per hour.
i.e.
We assume the data set has a bell-shaped distribution (i.e. Normal distribution).
To find : The percent of vehicles whose speeds are between 62 miles per hour and 70 miles per hour.
i.e . The percent of vehicles whose speeds are between miles per hour and miles per hour.
i.e . The percent of vehicles whose speeds are between miles per hour and miles per hour.
i.e. i.e . The percent of vehicles whose speeds are within one standard deviation from the mean.
According to the Empirical rule , about 68% of the population lies within one standard deviation of the mean.
It means , about 68% of vehicles lies within one standard deviation of the mean.
i.e . About 68% of vehicles whose speeds are between miles per hour and miles per hour.
i.e . About 68% of vehicles whose speeds are between miles per hour and miles per hour.
⇒ About 68% of vehicles whose speeds are between 62 miles per hour and 70 miles per hour.