5. LetX1,X2,X3,X4be iid rvs withE(Xi) =µand var(Xi) =s2>0, fori= 1,2,3,4.Consider the following four estimators ofµ:T1=13(X1+X2) +16(X3+X4)T2=16(X1+ 2X2+ 3X3+ 4X4)T3=14(X1+X2+X3+X4)T4=13(X1+X2+X3) +14X24(a) Which of these estimates are unbiased? Show your working.(b) Among the unbiased estimators, which one has the smallest variance?