## Re: How to find the mean and variance of 1/X?

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• THANK YOU VERY MUCH!
Message 1 of 5 , Nov 20, 2006
THANK YOU VERY MUCH!

--- In probability@yahoogroups.com, "zak_hi79" <zak_hi79@...> wrote:
>
> --- In probability@yahoogroups.com, wilson wu <wilsonwxwu@> wrote:
> >Dear Friend,
> I suggist to assume that y=1/x and make a transformation to this new
> r.v (y) and find f(y) then you can find the mean and variance.
>
> I will try to find it but it will take some times
> All my best
> ZAKaRIA
• ... new ... Hi If X 0, ie. X assumes only positive values and E(X) and E(1/X)exist then E(1/X) = 1/E(X)because 1/X is a convex function.
Message 2 of 5 , Nov 20, 2006
--- In probability@yahoogroups.com, "zak_hi79" <zak_hi79@...> wrote:
>
> --- In probability@yahoogroups.com, wilson wu <wilsonwxwu@> wrote:
> >Dear Friend,
> I suggist to assume that y=1/x and make a transformation to this
new
> r.v (y) and find f(y) then you can find the mean and variance.
>
> I will try to find it but it will take some times
> All my best
> ZAKaRIA
> > Excuse me.
> >
> > I have worked this question several days.
> >
> > Assume X follow a NORMAL distribution with mean A and variance B,
> how to find the the mean and variance of 1/X?
> >
> > Thank you very much.

Hi
If X >0, ie. X assumes only positive values and E(X) and E(1/X)exist
then E(1/X)>= 1/E(X)because 1/X is a convex function.

> >
> > Best wishes,
> >
> > Wilson
> >
> >
> > Wilson Weixing Wu
> >
> > School of Finance and Banking,
> > University of International Business and Economics,
> > Beijing 100029, China
> >
> >
> > Tel. 0086-10-64495048 (office)
> >
> > Fax. 0086-10-64495059
> >
> > Email: wxwu@
> >
> > Email: Wilsonwxwu@
> >
> > ---------------------------------
> > ÇÀ×¢ÑÅ»¢Ãâ·ÑÓÊÏä-3.5GÈÝÁ¿£¬20M¸½¼þ£¡
> >
> > [Non-text portions of this message have been removed]
> >
>
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