Question About Page 117

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#1 Vinicius-BR


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Posted 14 May 2012 - 05:32 PM


I was working on page 115 and when I compared the solutions there was something I didn't understand in your resolution.

The variance formula is not describe containing mean divided by n but in every resolution from pate 117 mean is added to 2000 (in the first resolution) or multiplied by 1.1 (in the second resolution) and it is already divided by n. Is it correct? shouldn't we multiply mean by n before we can make it the common denominator?

I will try to explain better bellow:

variance formula displayed on page 113:
(Ex^2)/n - M^2

variance used in first exercise resolution on page 117:
(E((x+2000) - (M + 2000))^2) / n
and in the second exercise on the same page:
(E((x*1.1) - (M*1.1))^2) / n

How did you added n as denominator for M without multiplying it? I'm trying to understand it but can't find a way.

Thanks for the help.

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