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 fit a model for which the true regression line passes through (0, 0). The appropriate model is Y = β1x + ε. Assume that (x1, y1, ... , (xn, yn) are observed pairs generated from this model, and derive the least squares estimator of β1?