find variance

**cm917** · April 30th 2009, 10:11 AM

Fx(x)= 0 , x<1
Fx(x)= (x^2-2x+2)/2 , 1<= x <2
Fx(x)=1, x>=2

calcualtae the variance of x.

I drew the graph of this function. it is a mixed distribution with a point-mass at 1. But i dont know how to solve it.....

**Moo** · April 30th 2009, 10:30 AM

Hello,

Find the pdf f of this function, by differentiating $F_X$

Then the variance is :
$\int_0^2 x^2 f(x) ~dx-\left(\int_0^2 x f(x) ~dx\right)^2$
(definition of the variance)

**matheagle** · April 30th 2009, 08:21 PM

Almost (certainly, not).
You're slipping, moo, you need the square.

Originally Posted by Moo

Hello,

Find the pdf f of this function, by differentiating $F_X$

Then the variance is :
$\int_0^2 x^2 f(x) ~dx-\left(\int_0^2 x f(x) ~dx\right)^{\color{red}2}$

This is the short cut formula for the variance.

The definition is $E\biggl(X-E(X)\biggr)^2$

Thread: find variance

LinkBack

Thread Tools

Display

find variance

Similar Math Help Forum Discussions

find the Variance

What is the best way to find the variance?

Find the Variance

Find variance of g(x)

Find mean and variance

Search Tags