# A little help

• September 22nd 2008, 06:17 AM
vish93
A little help
I haven't done stats in a long time....

I have a moment generating function for a r.v X as follows:

M(t) = Exp(2(e^t -1).

Is is possible to calculate Vav(e^x)?

Any suggestion?

Tks
• September 22nd 2008, 11:42 AM
CaptainBlack
Quote:

Originally Posted by vish93
I haven't done stats in a long time....

I have a moment generating function for a r.v X as follows:

M(t) = Exp(2(e^t -1).

Is is possible to calculate Vav(e^x)?

Any suggestion?

Tks

For the properties of the moment generating function see the Wikipedia page.

$Var(e^x)=E(e^{2x})-E(e^x)^2$

and:

$M(t)=E(e^{tx})$

so:

$Var(e^x)=M(2)-M(1)^2$

RonL
• October 2nd 2008, 03:45 PM
vish93
thanks
thaks for the helo