A random variable X with PMF given by

px(x) = {(x^2)/a, x=-3,-2,-1,0,1,2,3,

0 otherwise}

i believe a = 28 and E[X] = 0

am i right in thinking this?

What is the PMF of the random variable Y = (X-E[X])^2?

Use the random variable Y to find Var[X]

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- Oct 13th 2009, 10:28 AMsirellwoodRandom Variable PMF
A random variable X with PMF given by

px(x) = {(x^2)/a, x=-3,-2,-1,0,1,2,3,

0 otherwise}

i believe a = 28 and E[X] = 0

am i right in thinking this?

What is the PMF of the random variable Y = (X-E[X])^2?

Use the random variable Y to find Var[X] - Oct 13th 2009, 09:46 PMmatheagle
a=28 and moo is zero, I mean E(X), sry

and the distribution of X is...

P(X=-3)=P(X=3)=9/28

P(X=-2)=P(X=2)=4/28=1/7

P(X=-1)=P(X=1)=1/28

NOW, let

$\displaystyle Y=X^2$

So, P(Y=9)=P(X=-3)+P(X=3)=18/28=9/14

P(Y=4)=P(X=-2)+P(X=2)=2/7

and P(Y=1)=P(X=-1)+P(X=1)=1/14

E(Y)= 9(9/14)+4(2/7)+1(1/14), which better be the variance of X. - Oct 14th 2009, 02:33 PMsirellwood
thank you! makes sense, i understand now!