Marty and Ann discussed the rule of equal marginal utility per dollar spent, a topic that was recently covered in the economics course they were both taking: Marty: “When I use my calculator to divide the marginal utility of pizza by a price of zero, I don’t get an answer. This result must mean that if pizza were being sold for a price of zero, the quantity demanded would be infinite.”
Ann: “Marty, that can’t be true. No producer would be willing to ‘sell’ pizza, or any other product, for a zero price. Quantity demanded cannot be infinite, so zero prices cannot appear on demand curves and demand schedules.” Suppose that Marty and Ann ask you for advice in resolving their disagreement. What would you tell them?