pdf and variance

**dynas7y** · March 16th 2010, 11:29 AM

Solved

**Anonymous1** · March 16th 2010, 02:37 PM

[]EDIT[]The interval was unspecified. Please check the interval on which the density is defined and put it in place of [a,b]

$E[Y]= \int_{a}^{b} y \times 3(1-y)^2 dy$

$E[Y^2]= \int_{a}^{b} y^2 \times 3(1-y)^2 dy$

Also, $Var(Y) = E[Y^2] - (E[Y])^2$

and, $Var(W) = 25Var(Y)$

Use:

http://integrals.wolfram.com/index.jsp

to speed up your integration.
Anonymous

**matheagle** · March 16th 2010, 05:30 PM

clearly the region isn't all of $R^1$ so that integration is incorrect

NEXT comment, the region is most likely (0,1) and that means this is a Beta(1,3)
you can look up it's variance in that case.

**Anonymous1** · March 16th 2010, 05:42 PM

Yeah, it was unspecified so I just kinda went to default. Thanks for catching that.

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