- Within the context of a Production Possibilities Frontier (PPF) for a country producing military goods and civilian goods, what does the marginal cost of producing one additional military good represent?
Answer: The amount of civilian goods that must be foregone to produce that military good.
The PPF illustrates the concept of opportunity cost. When operating on the frontier (efficiently), producing more of one good requires producing less of another. The marginal cost of an additional military good is precisely the quantity of the other good (civilian goods) that must be sacrificed. This is also known as the marginal rate of transformation.
- A consumer values the first cup of coffee in a day at $5, the second at $3, and the third at $1. If the price of a cup of coffee is $2, a rational consumer buys two cups. Which statement provides the most accurate explanation for this choice based on marginal analysis?
Answer: The marginal benefit of the second cup ($3) exceeds its cost ($2), but the marginal benefit of the third cup ($1) is less than its cost.
Marginal analysis involves comparing the benefit and cost of each additional unit. The consumer buys the first cup because MB ($5) > MC ($2). They buy the second cup because MB ($3) > MC ($2). They do not buy the third cup because MB ($1) < MC ($2). This step-by-step comparison is the essence of marginal reasoning. While statement A is true, it describes the outcome (maximized surplus) rather than the marginal process used to arrive at that outcome.
- A software company spent $2 million developing a new application. After launch, sales are disappointing. The management team is now deciding whether to spend an additional $200,000 on a marketing campaign. The campaign is projected to generate $250,000 in new sales. Which of the following statements provides the correct marginal analysis of this decision?
Answer: The company should undertake the campaign because the marginal revenue of $250,000 is greater than the marginal cost of $200,000.
The correct decision-making process relies on marginal analysis. The $2 million development cost is a sunk cost and is irrelevant to the current decision. The marginal cost of the campaign is $200,000, and the marginal benefit (revenue) is $250,000. Since the marginal benefit exceeds the marginal cost, the campaign is a rational choice.
- A student has five hours available to prepare for two final exams: economics and physics. The first hour spent on economics increases their expected score by 10 points, while the first hour on physics increases it by 6 points. The second hour on economics adds 7 points, while the second hour on physics adds 5 points. To maximize their total score increase in the first two hours, the student should spend:
Answer: the first hour on economics, and the second hour also on economics.
The student should allocate each hour to the subject with the higher marginal benefit. For the first hour, the MB of economics (10 points) is greater than the MB of physics (6 points), so they should study economics. For the second hour, they must compare the MB of the second hour of economics (7 points) with the MB of the first hour of physics (6 points). Since 7 > 6, they should spend the second hour on economics as well. This yields a total gain of 10 + 7 = 17 points.
- A coffee shop currently employs two baristas during its morning rush. Hiring a third barista would cost $20 per hour in wages and benefits. The owner estimates that a third barista would allow the shop to serve more customers, increasing revenue by $35 per hour. However, a fourth barista would also cost $20 per hour but would only increase revenue by $15 per hour due to limited space behind the counter. What is the optimal number of baristas to hire?
Answer: Three baristas, because the marginal benefit of the third exceeds the marginal cost, but the opposite is true for the fourth.
Decisions are made at the margin. For the third barista, MB ($35) > MC ($20), so they should be hired. For the fourth barista, MB ($15) < MC ($20), so they should not be hired. Therefore, the optimal number of baristas is three. Distractor D incorrectly compares total additional revenue to total additional cost, which obscures the fact that the fourth hire is an unprofitable decision on its own.
- A movie enthusiast pays $15 for a monthly streaming subscription. This allows unlimited viewing of films. For this consumer, what is the marginal cost of watching one additional movie during the month?
Answer: Effectively zero, not including the opportunity cost of the consumer's time.
Once the $15 subscription fee is paid, it is a fixed cost for the month. The monetary cost of watching one more movie is zero. The relevant marginal cost for the consumer's decision to watch a specific movie is non-monetary: the opportunity cost of their time (i.e., what else they could be doing). The question focuses on the cost related to the service, which is zero at the margin.
- A consumer is searching online for the best price on a new television. They should continue to invest time in searching as long as:
Answer: the expected savings from one additional search query is greater than the opportunity cost of their time.
This is a marginal analysis of information gathering. The marginal cost is the opportunity cost of the time spent on one more search. The marginal benefit is the expected price reduction from that search. A rational consumer will stop searching when the marginal cost of searching outweighs the expected marginal benefit.
- An airline is deciding whether to sell a standby ticket on a flight that is about to depart with a few empty seats. The full fare for a seat is $500, and the average cost per seat (including fuel, crew, and overhead) is $300. The airline should sell a standby ticket for any price that is:
Answer: above the marginal cost of flying one extra passenger, which is close to zero.
For a flight that is about to depart with empty seats, most costs (fuel, crew, airport fees) are fixed and sunk. The marginal cost of adding one more passenger is extremely low—perhaps just the cost of a beverage and a small amount of extra fuel. Therefore, any revenue above this very low marginal cost will add to the airline's profit (or reduce its loss) from the flight. The average cost and full fare are not relevant to this specific marginal decision.
- A city council votes to build a new bridge. The total expected benefit to the community is estimated at $50 million, and the total cost of construction is $40 million. Which of the following statements is necessarily true based on this information?
Answer: The project is economically justified because the total benefit exceeds the total cost.
The information provided compares total benefits and total costs. Since total benefits ($50M) are greater than total costs ($40M), the project as a whole is justified. However, this does not mean the decision was made optimally at the margin. It is possible that the bridge is larger than it should be (e.g., the last lane added more to cost than to benefit), so we cannot be sure about statement C or D. Statement A misuses the term 'marginal benefit' to refer to the total benefit of the entire project.
- A student is studying for an exam. The first hour of studying is very productive, but each subsequent hour results in less learning (diminishing marginal benefit). Simultaneously, each additional hour of studying increases fatigue and stress (increasing marginal cost). The student should stop studying at the point where:
Answer: the benefit gained from one additional hour of study equals the wellness cost of that specific hour.
The optimal duration of an activity is where the marginal benefit (MB) equals the marginal cost (MC). In this case, the student should continue studying as long as the benefit from an additional hour exceeds the cost of that hour. The stopping point is where MB = MC. Options A, C, and D describe suboptimal decision rules that ignore either the marginal nature of the choice, the cost, or both.
- A city is considering a policy to reduce traffic congestion by imposing a $5 toll on a bridge during peak hours. From the perspective of a driver making a single trip, how does this toll alter the decision-making process?
Answer: It increases the marginal cost of crossing the bridge, making the driver less likely to take the trip.
The toll is an additional cost for each trip, so it directly increases the marginal cost of crossing the bridge. A rational driver compares the marginal benefit of their trip to the marginal cost (fuel, time, and now the toll). By increasing the marginal cost, the toll will cause some drivers, for whom the marginal benefit was previously greater than the cost but is now less, to choose not to cross.
- A firm that produces luxury watches finds that producing its 100th watch per month will cost $5,000. Due to its market power, selling this 100th watch requires the firm to lower the price on all its watches from $8,000 to $7,900. What is the economically rational course of action for the firm?
Answer: Do not produce the 100th watch because its marginal revenue is negative and therefore less than its marginal cost.
The decision should be based on comparing marginal revenue (MR) and marginal cost (MC). MC = $5,000. MR must be calculated. Original total revenue (99 watches): 99 $8,000 = $792,000. New total revenue (100 watches): 100 $7,900 = $790,000. The marginal revenue of the 100th watch is $790,000 - $792,000 = -$2,000. Since MR (-$2,000) is less than MC ($5,000), the firm should not produce the 100th watch.
- A high school senior has been accepted to two universities. University A is a top-ranked school with a tuition of $50,000 per year. University B is a reputable state school with tuition of $20,000 per year. In making a rational decision, the student should choose University A only if:
Answer: the perceived marginal benefit of attending A over B is at least $30,000 per year.
The decision is a choice between two options. The marginal cost of choosing A over B is the difference in tuition, which is $50,000 - $20,000 = $30,000 per year. The marginal benefit is the additional value (in terms of future earnings, networking, experience, etc.) gained by attending A instead of B. A rational decision requires the marginal benefit to be greater than or equal to the marginal cost.
- A farmer is deciding how much fertilizer to use on a field. The first ton increases crop yield by 100 bushels. The second ton increases yield by an additional 80 bushels. The third ton increases yield by an additional 50 bushels. If the price of a bushel of the crop is $10 and the price of a ton of fertilizer is $600, how many tons should the farmer use?
Answer: Two tons, because the marginal benefit of the second ton ($800) still exceeds its cost.
The farmer should compare the marginal benefit (MB) and marginal cost (MC) for each ton. MC = $600. MB of 1st ton = 100 bushels $10/bushel = $1,000. Since MB > MC, use the first ton. MB of 2nd ton = 80 bushels $10/bushel = $800. Since MB > MC, use the second ton. MB of 3rd ton = 50 bushels * $10/bushel = $500. Since MB < MC, do not use the third ton. The optimal quantity is two tons. Distractor C shows a common error of using total benefit/cost instead of marginal.
- A student has an average grade of 85 after completing 4 assignments for a class. If the student completes a fifth assignment and earns a grade of 75, what is the direct effect on their average grade and what does the grade of 75 represent in economic terms?
Answer: The average will decrease, and the 75 represents the marginal benefit of the fifth assignment.
The grade of 75 on the fifth assignment is the marginal benefit (or marginal product) of the effort on that specific assignment. Since this marginal benefit (75) is lower than the previous average (85), it will pull the average down. The total score would go from 4*85=340 to 340+75=415, for a new average of 415/5=83.
- An individual is considering purchasing a warranty for a new laptop. The warranty costs $100. The individual believes there is a 10% chance the laptop will break, which would cost $800 to repair. The decision to buy the warranty is rational if the individual's:
Answer: perceived marginal benefit of avoiding the potential $800 loss is greater than the $100 marginal cost.
The decision hinges on comparing the marginal cost (the $100 price of the warranty) with the marginal benefit (the peace of mind or risk avoidance it provides). While the expected monetary cost of a breakdown is $80, a risk-averse person may value avoiding the possibility of an $800 loss at more than $100. Therefore, if the perceived benefit of eliminating that risk is greater than the $100 cost, the purchase is rational. This tests the conceptual nature of marginal benefit, which can be subjective.
- A beekeeper's hives provide a pollination benefit to a neighboring apple orchard, which is a positive externality. The beekeeper makes decisions about the number of hives to keep based solely on her own costs and the revenue from honey. From a social efficiency perspective, the beekeeper's decision results in an outcome where:
Answer: the social marginal benefit of the hives is greater than the beekeeper's private marginal benefit.
The social marginal benefit is the sum of the private marginal benefit (the beekeeper's revenue) and the external marginal benefit (the value of pollination for the orchard). Because the external benefit is positive, the social marginal benefit is greater than the private marginal benefit. The beekeeper, considering only her private benefit, will maintain fewer hives than is socially optimal.
- A government agency is funding a public health initiative. It has determined that the first million dollars spent prevents 1,000 illnesses. The second million prevents an additional 800 illnesses, and the third million prevents an additional 500. This pattern illustrates the concept of:
Answer: diminishing marginal benefit of public health spending.
Marginal benefit is the additional benefit from one more unit of an input. Here, the input is '$1 million in spending' and the benefit is 'illnesses prevented'. Because each successive million dollars yields a smaller number of prevented illnesses than the one before it (1000 -> 800 -> 500), this demonstrates diminishing marginal benefit.
- A freelance graphic designer is deciding whether to take on one more project before going on vacation. The project pays $500 and will take 10 hours of work. The designer values her leisure time at $30 per hour. Which of the following represents the marginal cost that she should weigh against the $500 payment?
Answer: The $300 value of the 10 hours of leisure she must give up to complete the project.
The marginal benefit of the project is the $500 payment. The marginal cost is the opportunity cost of her time. In this case, the best alternative use of her time is leisure, which she values at $30/hour. Therefore, the marginal cost of the 10-hour project is 10 hours * $30/hour = $300. Since MB ($500) > MC ($300), she should take the project. Taxes reduce the net marginal benefit but are not the marginal cost itself.
- A restaurant is open for lunch and is deciding whether to stay open for dinner. The restaurant's daily rent is $300. The variable costs for serving dinner (staff, ingredients) would be $400, and the expected revenue from dinner is $600. Which statement best describes the correct decision and reasoning?
Answer: Stay open for dinner, because the marginal revenue of $600 exceeds the marginal (variable) cost of $400.
In a short-run decision like this, fixed costs (rent) are considered sunk. The decision should be made by comparing the marginal revenue and marginal cost of the action. The marginal revenue from staying open is $600. The marginal cost is the variable cost of $400. Since MR > MC, staying open is profitable at the margin and will generate a $200 contribution towards fixed costs, reducing the day's overall loss.
