Suppose that x1 and x2 are random samples of observations from a population with mean m and variance s 2 . Consider the following three point estimators, A, B, C, of m: A = x1 + x2 2 , B = x1 + 3x2 4 , C = x1 + 2x2 3 .

a) Which of these estimators yields an unbiased estimator of m? Justify your answer.#

b) Of those that are unbiased, which is the most efficient? Justify your answer.