Question A firm has a large number of accounts; 40% of its accounts receivable are wholesale and 60% are retail.

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Part a) Find an unbiased estimate of the population mean ¯yU . Suppose that the sample standard deviation is s = 170, estimate the variance of your unbiased estimator. (Ignore finite sample corrections)

Part b) Suppose one treats the sample as a stratified random sample with proportional allocation. Re-estimate ¯yU using stratified sample mean and estimate the variance of this estimator. (Ignore finite sample corrections)