Question 1209505
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For "standard deviation" and for "Sample standard deviation" 
(they are two different notions/conceptions) read in this source


<A HREF=https://www.calculator.net/standard-deviation-calculator.html>https://www.calculator.net/standard-deviation-calculator.html</A>


https://www.calculator.net/standard-deviation-calculator.html



It is written there in a short, clear and comprehensive form.



It is also written in any textbook on Probability and/or Statistics,

so it is even strange to me that somebody comes with the question, to which they 

should know the answer as a pre-requisite, from authoritative sources, without my help.



It is the same as to come to me and ask "what is the equation for 2 x 2 ?"



Or, may be, you do not trust to your textbook ?


Or, may be, you expect that I will re-write page after page from a textbook 
for you to satisfy your curiosity ?


Or, may be, you are in process of creating your own textbook, 
collecting pieces from volunteer tutors from various web-sites ?



One can see all sorts of things at this forum . . .