THE EMPIRICAL RULE
For normally distributed data there will be approximately 68% of the data within one standard deviation of the mean, approximately 95% of the data within two standard deviations of the mean, and approximately 99.7% of the data within three standard deviations of the mean.
There are two example problems.
Example 1: JUSTIFYING THE EMPIRICAL RULE
Example 2: USING THE EMPIRICAL RULE