28. Suppose an investigator has data on the amount of shelf space x devoted to display of a particular product and sales revenue y for that product. The investigator may wish to t a model for which the true regression line passes through (0, 0). The appropriate model is Y  b1x 

e. Assume that (x1, y1), . . . , (xn, yn) are observed pairs generated from this model,

and derive the least squares estimator of b1. (Hint:
Write the sum of squared deviations as a function of b1, a trial value, and use calculus to nd the minimizing value of b1.)