Solve using variance and not standard error.

Problem 2. (Problem 10.4 page 194) Suppose that we have independent samples of size 10 and 15, respectively, from a population with mean u. We calculate the sample mean for each sample and refer to them as X10 and X15. a. Is X10 or X15 a better estimator of u? Fully justify your answer. b. Consider the following ways of combining X10 and X15 to form a single estimate of /: 01 = ~X10 + - X15 10 02 - 25 15 X10 + 25 X 15 The difference has to do with whether the sample means are equally weighted or given differential weights based upon the different sample sizes. Which estimator is better? Fully justify your