A monopolist operates in an industry where the demand curve is given byQ= 100 -P. The monopolist's constant marginal cost is $20.Using IEPR, derive the price elasticity of demand at the profit-maximizing price.

Assume that there is no fixed cost of production. Using a two-panel graph, show the profit-maximizing condition of this monopolist, clearly indicating the profit-maximizing quantity and price. In both panels use the same scale to measure the quantity. In the first panel, draw the monopolists TC, TR, and profit functions. In the second panel, draw the monopolists, AR, MR, and MC functions.