Let X1, X2 be a random sample of size 2 from a population X with E(X)=mu and V(X) = 36. Let T1 = (2X1 + X2)/3 and T2 = (3X1 - X2)/3 be two unbiased estimators for mu.
a) Find V(T2)
b) Given V(T1) = 20, select (say why) the estimator you prefer among T1 and T2.