# pdf and variance

• March 16th 2010, 12:29 PM
dynas7y
pdf and variance
Solved
• March 16th 2010, 03:37 PM
Anonymous1
[]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

Anonymous
• March 16th 2010, 06:30 PM
matheagle
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.
• March 16th 2010, 06:42 PM
Anonymous1
Yeah, it was unspecified so I just kinda went to default. Thanks for catching that.