Figure 5-3 A graph of price, P, versus quantity, Q, is a demand curve consisting of a straight line descending from (0, 100) to (50, 0). The following points are shown. (5, 90), (10, 80), (15, 70), (20, 60), (25, 50), (30, 40), (35, 30), (40, 20), (45, 10). Refer to Figure 5-3. Using the midpoint method, between prices of $20 and $30, price elasticity of demand is about a. 3. b. 1.33. c. 0.4. d. 0.33