1. [24 points] An advertising firm is concerned with the effect of a new promotional campaign on the total dollar sales for a particular product. A simple random sample of 20 stores is drawn from the 450 stores in which the product is sold. Quarterly sales data are obtained for the current three-month period and the three-month period prior to the new campaign. The sample data on the 20 stores are summarized as follows. Sample mean Sample variance Sample covariance Pre-campaign sales 48 679 713 Present sales 51 751 The total sales for the pre-campaign period is known to be 21626. (1) [8 points] Estimate the total sales for the current period using the simple/ unbiased estimator, and place a bound on the error of estimation.(2) [8 points] Estimate the total sales for the current period using the ratio estimator, and place a bound on the error of estimation. (3) [8 points] Estimate the total sales for the current period using the regression estimator, and place a bound on the error of estimation