Here's the problem that I am having.

Let X and Y be random variables with E(X)=1, E(Y)= 4 Var(X)= 4 Var(Y)=6 p=1/2. Find mean and variance of Z= 3X-2Y.

I found the mean. I just need help finding Var(Z). Please help me out. Thanks.

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- August 3rd 2008, 09:05 AMhelium0204Issues With Expectations
Here's the problem that I am having.

Let X and Y be random variables with E(X)=1, E(Y)= 4 Var(X)= 4 Var(Y)=6 p=1/2. Find mean and variance of Z= 3X-2Y.

I found the mean. I just need help finding Var(Z). Please help me out. Thanks. - August 3rd 2008, 01:57 PMMoo
Hello,

For this, you have to remember that the mean is a linear function, that is to say E(aX+bY)=aE(X)+bE(Y)

For the variance, the formula is : var(aX+bY)=a^2 var(X)+b^2 var(Y), assuming that X and Y are independent. Otherwise you will need more information.

You can prove this formula with the definition of the variance that includes the mean :

var(X)=E(X^2)

and var(X+Y)=var(X)+var(Y) if X and Y are independent.

Edit : What is p ??? - August 3rd 2008, 02:52 PMhelium0204
- August 3rd 2008, 04:48 PMMoo