The variance is easy since they're all independent (hence the variance of their sum is the sum of their variance)
LetX1, · · · ,Xn be independent random variables with E(Xi) = μ and V (Xi) = sigma^2. Also,let ¯X be the sample mean. Then Cov(Xi − ¯X , ¯X) = c. What is the numerical value of c ? (Your answer should not depend on n, μ, or sigma)
I have no clue how to do this question...any help will be greatly appreciated!