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The following is a question regarding statements from "Chemical Fate and Transport in the Environment" 2e by Hemond and Fechner-Levy pg. 78. I do not understand point #2 that follows, if anyone can point me to a proof or literature that explains this property I'd greatly appreciate it!

1) "It follows from the properties of the normal distribution that the portion of the distribution within one standard deviation of the mean value (both + and -) includes 68% of the possible values. [I understand this]

2) "It also follows that the value at one standard deviation from the mean value is equal to the mean value multiplied by 0.61" [This is the statement I am having trouble understanding]

Thanks!

I recently saw a map of the usa that had nuclear facilities overlaid and noticed a cluster in illinois. So my question is did the state of Illinois offer incentives or some other attraction to nuclear operators to develop in the state?