5. Let X be a random variable with E(X) = M and Var(X) = 62 We have information about four iid observations: X1, X2, X3, X4. Let All = = (X1 + X2 + X3 + X4) be an estimator for the population mean. a) What are the expected value and variance of / in terms of M and o?? b) Now consider a second estimator for the population mean /2 being defined as: A12 = X1 X2 X3 -X4 2 Show that this second estimator is also an unbiased estimator for the population mean. Find its variance. c) Discuss the sufficiency of both estimators. d) Based on all your previous answers, which estimator do you prefer