In: Statistics and Probability
Let X1,...,Xn be independent random variables,and let X=X1+...+Xn be their sum.
1. Suppose that each Xi is geometric with respective parameter pi. It is known that the mean of X is equal to μ, where μ > 0. Show that the variance of X is minimized if the pi's are all equal to n/μ.
2. Suppose that each Xi is Bernoulli with respective parameter pi. It is known that the mean of X is equal to μ, where μ > 0. Show that the variance of X is maximized if the pi's are all equal to μ/n.