IEU Let U be a population of size N which is partitioned into 2 strata U and U, of size N and N, respectively. Let J = N Liet, and Ju = N Liet denote the stratum means of a survey variable y in both strata. In stratum h, h = 1.2, we select a simple random sample without replacement Sh, of size n, h = 1,2. The sample selection in Stratum 1 is independent from the sample selection in Stratum 2. (a) Suppose that we want to estimate the difference D = JU1-2. Propose an unbiased estimator of D (call it D) and determine its variance. 1 (b) Suppose that we want to estimate the product P = JUIX 2. Propose an unbiased estimator of P (call it P) and determine its variance.