68–95–99.7 rule - Wikipedia
https://en.wikipedia.org/wiki/68%E2%80%9395%E2%80%9399.7_rule
WEBIn statistics, the 68–95–99.7 rule, also known as the empirical rule, is a shorthand used to remember the percentage of values that lie within an interval estimate in a normal distribution: 68%, 95%, and 99.7% of the values lie within one, two, and three standard deviations of the mean, respectively. In mathematical notation, these facts ...
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