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- Mar 16th 2010, 11:29 AMdynas7ypdf and variance
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- Mar 16th 2010, 02:37 PMAnonymous1
[]EDIT[]The interval was unspecified. Please check the interval on which the density is defined and put it in place of [a,b]

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

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

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

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

Use:

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

to speed up your integration.

Anonymous - Mar 16th 2010, 05:30 PMmatheagle
clearly the region isn't all of $\displaystyle R^1$ 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. - Mar 16th 2010, 05:42 PMAnonymous1
Yeah, it was unspecified so I just kinda went to default. Thanks for catching that.