# Math Help - Expected Value and Variance?

1. ## Expected Value and Variance?

Let X1, X2…..X10 be such that E(Xi) = 2/3 for all i, Var(Xi) = 2/9 for all i, and Cov(Xi,Xj)=-1/63 for all i and j with i=/=j. Let X=X1+ X2+…….+X10.
Find E(X) and Var(X).

I have no idea how to begin.

Thanks

2. ## Re: Expected Value and Variance?

Originally Posted by blackZ
Let X1, X2…..X10 be such that E(Xi) = 2/3 for all i, Var(Xi) = 2/9 for all i, and Cov(Xi,Xj)=-1/63 for all i and j with i=/=j. Let X=X1+ X2+…….+X10.
Find E(X) and Var(X).

I have no idea how to begin.

Thanks
Start by going to the formulas you will have been given in your class notes and textbook and applying them. Show all your work, say exactly where you are stuck.