Normal distribution/Gaussian distribution has many applications. All normal density curves satisfy the following property:

- 68% of the observations fall within 1? of the mean, that is, between ? – ? and ? + ?.
- 95% of the observations fall within 2? of the mean, that is, between ? – 2? and ? + 2?.
- 99.7% of the observations fall within 3? of the mean, that is, between ? – 3? and ? + 3?.
- Almost all values lie within 3 standard deviations of the mean.