The marginal utility graph for both would be negative because the marginal utility per hamburger and the marginal utility per milkshake both decrease as the quantity consumed increases. Both graphs would also approximate a curve because the change in marginal utility is not constant as the quantity consumed increases; for both graphs, the change is greater between the first two units consumed than between the last two units consumed. In addition, because the overall change in the marginal utility of hamburgers is greater than the change in the marginal utility of milkshakes, the hamburger curve would be steeper than the milkshake curve.

What will be an ideal response?

: (1) a situation in which using a rule of thumb led to an optimal result, such as ordering the burger off a menu at a new restaurant because you EXPECT the odds are low that any restaurant would make a bad burger (and you were right!), and (2) a situation in which using a rule of thumb led to a less-than-optimal result, such as when you bought a faulty refrigerator because you did not have time to do research and made the purchase based on the brand name. Students should recognize that in both situations, they used a rule of thumb because they lacked time or information to thoroughly weigh the marginal utility of their choices (bounded rationality). They should also recognize that not all rules of thumb lead to optimal outcomes: in one situation it helped them maximize their utility, whereas in the other it did not.