Let x represent the scores. With mean and standard deviation given,
The Empirical rule states that
1) About 68% of the x values lie between 1 standard deviation below and above the mean
2) About 95% of the x values lie between 2 standard deviation below and above the mean
3) About 99.7% of the x values lie between 3 standard deviation below and above the mean
If we consider this rule, then the percentage of scores that fall within 3 standard deviation (-3 to +3) is 99% because this is closer to 99.7%
