Supply and Demand: Beyond the Basics

• A. Price elasticity of demand
• B. Income elasticity of demand ✓
• C. Cross-price elasticity of demand
• D. Price elasticity of supply

Why: Income elasticity of demand measures the percentage change in quantity demanded divided by the percentage change in consumer income, capturing how demand shifts as households earn more or less.

• A. A normal good
• B. A luxury good
• C. An inferior good ✓
• D. A complementary good

Why: A negative income elasticity means quantity demanded falls when income rises, which is the defining feature of an inferior good, such as generic instant noodles for many households.

• A. They are complements
• B. They are substitutes ✓
• C. They are both inferior goods
• D. They are unrelated goods

Why: A positive cross-price elasticity means that when the price of one good rises, the quantity demanded of the other rises too, which indicates the goods are substitutes like coffee and tea.

• A. Consumers have more time to adjust by buying fuel-efficient cars or changing where they live ✓
• B. Gasoline becomes a necessity over time
• C. Gasoline producers change their supply schedules
• D. Income effects disappear over time

Why: In the short run, consumers have limited options and must keep driving, so demand is relatively inelastic. Over time they can switch to more efficient vehicles, carpool, or move closer to work, making demand more elastic.

• A. Positive
• B. Zero
• C. Negative ✓
• D. Infinite

Why: Complements are goods used together, so when the price of printers rises, the quantity demanded of ink falls. This inverse relationship produces a negative cross-price elasticity.

• A. Marginal revenue equals price at every quantity sold.
• B. Marginal revenue falls below the price at every quantity sold. ✓
• C. Marginal revenue rises as output increases.
• D. Marginal revenue is always negative.

Why: A monopolist must lower the price on all units to sell an additional unit, so the revenue gained from one more unit is less than the price charged. This makes marginal revenue lie below the demand curve. A competitive firm takes price as given, so its marginal revenue equals price.

• A. It charges the minimum point of its average cost curve.
• B. It charges the price on the demand curve corresponding to that quantity. ✓
• C. It charges the price equal to its marginal cost.
• D. It charges whatever price matches the competitive market price.

Why: The monopolist chooses quantity where MR = MC, then uses the demand curve to find the highest price consumers will pay for that quantity. Price is not set equal to marginal cost, which would be the competitive outcome.

• A. Many small sellers offering identical products.
• B. Free and easy access to all necessary inputs for new firms.
• C. Exclusive ownership of a key resource. ✓
• D. Consumers having perfect information about all sellers.

Why: Exclusive control of a key input prevents potential rivals from producing, which is a classic source of monopoly power. Legal protection such as patents and government franchises are also barriers. The other options describe conditions that promote competition rather than restrict entry.

• A. Total output is lower and price is higher.
• B. Total output is higher and price is lower. ✓
• C. Total output and price are both unchanged.
• D. Total output is higher but price is also higher.

Why: With competing firms each restricting output less than a single monopolist would, total industry output rises and the market price falls relative to monopoly. The outcome lies between monopoly and perfect competition, closer to competition as the number of firms grows.

• A. Each firm gains more profit by cooperating, but has an incentive to undercut the other, leading both to lower prices and lower profits. ✓
• B. Each firm always earns zero profit regardless of its pricing choice.
• C. Consumers force firms to lower prices through boycotts.
• D. Government regulation requires firms to match each other's prices exactly.

Why: Collusion at high prices would maximize joint profits, but each firm can grab extra customers by undercutting. When both act on this incentive, they settle at a lower-price equilibrium where both earn less, which is the prisoner's dilemma logic applied to oligopoly.

• A. A positive externality
• B. A negative externality ✓
• C. A public good
• D. A merit good

Why: A negative externality occurs when a transaction imposes uncompensated costs on third parties. Here, the factory's production harms downstream residents, who bear costs the factory does not pay for.

• A. It is rival and excludable
• B. It is rival but non-excludable
• C. It is non-rival and non-excludable ✓
• D. It is non-rival but excludable

Why: Pure public goods are non-rival (one person's consumption does not reduce availability to others) and non-excludable (it is impossible or very costly to prevent people from using it), such as national defense or clean air.

• A. More than the socially optimal quantity
• B. Exactly the socially optimal quantity
• C. Less than the socially optimal quantity ✓
• D. The quantity is unrelated to externalities

Why: Individuals consider only the private benefit when deciding how much to consume. Because the social benefit (including benefits to others) exceeds the private benefit, the market underproduces relative to the socially optimal level.

• A. When a good is rival and excludable, such as a sandwich
• B. When people can benefit from a good without paying for it, as with public goods ✓
• C. When a monopolist restricts output to raise prices
• D. When consumers have perfect information about prices

Why: The free-rider problem occurs when non-excludability allows people to consume a good without contributing to its cost. This leads private markets to underprovide public goods, since rational individuals hope others will pay.

• A. A subsidy for polluting firms
• B. A Pigouvian tax equal to the marginal external cost ✓
• C. A price ceiling on the polluting good
• D. A reduction in the number of regulations

Why: A Pigouvian tax is set equal to the marginal external damage, internalizing the externality so producers account for social costs. Subsidies would worsen the problem, and price ceilings do not address the underlying cost imbalance.

• A. Sellers always charge prices that are too low for buyers to afford
• B. Buyers cannot distinguish high-quality goods from low-quality goods, so they are only willing to pay an average price, which drives high-quality sellers out of the market ✓
• C. Buyers have too much information, causing them to demand discounts on every product
• D. Government regulation forces all goods to be sold at the same price regardless of quality

Why: When buyers cannot verify quality, they offer a price reflecting the expected average quality. Sellers of above-average goods find this price too low and withdraw, lowering the average quality further and potentially unraveling the market.

• A. A car with a full service history and a warranty
• B. A car whose seller knows about hidden mechanical defects that the buyer cannot easily detect ✓
• C. A new car sold at the manufacturer's suggested retail price
• D. A car that the buyer has already inspected with a mechanic

Why: A lemon is a low-quality good whose defects are hidden from the buyer but known to the seller. This asymmetry of information is the defining feature of the lemons problem.

• A. Eliminating all warranties so sellers have no incentive to disclose quality
• B. Signaling, such as offering warranties or money-back guarantees that high-quality sellers can afford but low-quality sellers cannot ✓
• C. Requiring buyers to purchase goods without any inspection
• D. Setting a single fixed price for all goods regardless of their characteristics

Why: Warranties and guarantees are costly signals. High-quality sellers expect few claims and can afford to offer them, which credibly communicates quality to buyers and helps restore trade.

• A. Buyers selecting the cheapest product available regardless of quality
• B. The tendency for the mix of goods or participants in a market to skew toward lower quality because high-quality participants withdraw when they cannot be fairly priced ✓
• C. Governments selecting which firms are allowed to sell products
• D. Sellers choosing to advertise only their best products

Why: Adverse selection describes how information asymmetry causes the composition of a market to worsen, as the participants most harmed by underpricing (high-quality sellers) exit, leaving a higher share of low-quality goods.

• A. Because buyers enjoy bargaining and always start with low offers
• B. Because the buyer cannot tell whether the car is high or low quality, so the offer must reflect the expected average value across all cars for sale ✓
• C. Because sellers are legally required to accept any offer below market value
• D. Because high-quality used cars are always more expensive to maintain

Why: Since the buyer cannot distinguish quality, the rational offer is based on the average expected value of cars in the market, which is pulled down by the presence of lemons. This means good cars may be underpriced.

• A. It prevents the firm from selling any additional units until production catches up.
• B. It allows the firm to meet part of the extra demand immediately by drawing down stock, so the supply response is faster than production alone would allow. ✓
• C. It makes supply perfectly inelastic regardless of time horizon.
• D. It reduces the firm's incentive to raise prices when demand rises.

Why: Inventories act as a buffer: when demand rises unexpectedly, firms can sell from stock immediately, so quantity supplied rises faster than new production can be arranged. Option A is wrong because inventory enables additional sales, not blocks them.

• A. Supply becomes highly elastic because the firm can simply produce more.
• B. Supply becomes nearly vertical, so price rises substantially while quantity supplied barely changes. ✓
• C. Supply shifts to the right by the full amount of the demand increase.
• D. Supply becomes negatively sloped as costs fall with higher volume.

Why: At full capacity the firm cannot expand output in the short run, so the supply curve becomes steep, near vertical. Additional demand is absorbed mainly through higher prices rather than higher quantities.

• A. It makes supply more elastic in the short run because firms respond instantly.
• B. It makes supply less elastic in the short run because firms cannot quickly obtain additional inputs. ✓
• C. It has no effect because supply elasticity depends only on price.
• D. It shifts demand rather than supply.

Why: When inputs take a long time to arrive, firms cannot ramp up output quickly after a price rise, so short-run quantity supplied responds weakly and supply is less elastic.

• A. A bakery that can easily hire extra part-time staff within a day.
• B. A hotel with all rooms booked during a festival, unable to add rooms quickly. ✓
• C. A farmer who decides to plant a different crop next season.
• D. A retailer who lowers prices during a sale.

Why: A hotel with every room booked cannot quickly build new rooms, so its physical capacity limits how much it can supply in the short run. The other options describe flexible or long-run adjustments.

• A. Capacity constraints become more binding because firms cannot adjust them.
• B. Firms can expand capacity and rebuild inventories, making supply more elastic. ✓
• C. Inventories become irrelevant and supply becomes perfectly inelastic.
• D. Supply becomes less elastic because lead times grow indefinitely.

Why: Over longer periods firms can build new plants, add equipment, and adjust inventory levels, so capacity constraints loosen and supply becomes more elastic than in the short run.

• A. The tendency for prices to fall as more sellers enter the market
• B. The phenomenon where a product becomes more valuable to each user as the number of other users increases
• C. The decline in demand caused by overlapping product features
• D. The fixed cost advantage enjoyed by firms that produce at large scale

• A. A video game console becoming cheaper as production volume rises
• B. A messaging app becoming more useful as more of your friends join it
• C. A city's traffic congestion increasing with population growth
• D. A grocery store lowering prices during a seasonal sale

• A. Users on one side of the platform benefit from the presence of users on the other side
• B. Two competing platforms merging into a single firm
• C. A platform charging the same fee to all of its users
• D. Demand for a product falling as consumers switch to substitutes

• A. Because marginal costs rise sharply as the platform grows
• B. Because network effects make larger platforms more attractive, reinforcing their lead over smaller rivals
• C. Because government regulation always limits platforms to a single firm
• D. Because consumers prefer to use multiple platforms simultaneously

• A. Raising prices to signal high quality to early adopters
• B. Subsidizing one side of the market, such as offering free or discounted access, to attract users who then draw in the other side
• C. Restricting access so that only a small group can join at first
• D. Avoiding any investment in product quality until demand is proven

• A. A surplus of apartments as landlords supply more units
• B. A shortage of apartments as quantity demanded exceeds quantity supplied ✓
• C. No change in the quantity of apartments rented
• D. A decrease in demand for apartments as renters move elsewhere

Why: A binding price ceiling set below equilibrium keeps the price artificially low, so quantity demanded rises while quantity supplied falls, creating a shortage.

• A. Sellers bear the entire burden because they pay the tax
• B. Buyers bear the entire burden because they pay higher prices
• C. The burden is split between buyers and sellers, depending on the relative elasticities of supply and demand ✓
• D. The burden falls only on the government, which collects the revenue

Why: Who legally pays the tax does not determine who bears its economic burden. The incidence depends on relative elasticities: the less elastic side bears more of the tax.

• A. Price rises and quantity falls
• B. Price falls and quantity rises
• C. Both price and quantity rise ✓
• D. Both price and quantity fall

Why: A subsidy lowers producers' effective cost, shifting supply outward. This raises the equilibrium quantity, and the price paid by consumers typically falls, though the exact price change depends on elasticities. Consumers' price may fall, but the question's correct answer emphasizes that the quantity rises.

• A. Consumers gain surplus at the expense of producers with no inefficiency
• B. Some mutually beneficial trades between buyers and sellers no longer occur, reducing total surplus ✓
• C. Total surplus increases because prices are lower
• D. Producer surplus increases while consumer surplus is unchanged

Why: Price controls reduce the quantity traded below the efficient level, so some trades that would have benefited both parties are lost, creating deadweight loss.

• A. Employers hire more workers because wages are higher
• B. The higher wage reduces the quantity of labor demanded while increasing the quantity of labor supplied ✓
• C. Workers voluntarily leave the labor market when wages rise
• D. The price floor shifts labor demand to the right

Why: A price floor above equilibrium raises the wage above the market-clearing level. Employers demand less labor at the higher wage, while more people want to work, creating a surplus of labor, or unemployment.