📖 经济学综合模拟测试（20 题）

Economics

I. Lesson Focus

This lesson provides a comprehensive review and mock assessment of all major Economics topics tested at CFA Level I. It integrates microeconomic principles (demand and supply, elasticity, market structures, cost analysis), macroeconomic frameworks (AD-AS model, monetary and fiscal policy, growth, inflation and unemployment), and international economics (comparative advantage, balance of payments, exchange rate determination). The focus is on building the ability to quickly identify the relevant concept, apply the correct formula, and avoid common conceptual traps under timed conditions.

II. The Problem

Economics represents 14–20% of the CFA Level I exam. Candidates frequently lose marks on elasticity calculations, distinguishing between different market structures in the long run, transmission mechanisms of monetary versus fiscal policy, the effects of supply versus demand shocks in the AD-AS model, and the nuances of purchasing power parity versus interest rate parity. This 20-question mock, accompanied by detailed concept review and worked examples, allows candidates to diagnose weaknesses, reinforce quantitative skills, and internalize the precise conditions and assumptions behind each theory.

III. Core Microeconomic Framework Review

Microeconomics studies the decisions of individual consumers and firms and their impact on resource allocation. Key tools include demand and supply, elasticity, consumer theory, production and costs, and market structures.

Demand and Supply Equilibrium
The market demand curve slopes downward; the supply curve slopes upward. Equilibrium price occurs where quantity demanded equals quantity supplied. An increase in demand raises both equilibrium price and quantity. An increase in supply lowers price and raises quantity.

Elasticity
Price elasticity of demand measures responsiveness of quantity to price changes:
$E_d = \frac{\% \Delta Q_d}{\% \Delta P}$
- $|E_d| > 1$: elastic
- $|E_d| < 1$: inelastic
- $|E_d| = 1$: unit elastic

Income elasticity $E_I = \frac{\% \Delta Q_d}{\% \Delta I}$ distinguishes normal goods (>0) from inferior goods (<0).
Cross-price elasticity $E_{XY} = \frac{\% \Delta Q_X}{\% \Delta P_Y}$ is positive for substitutes and negative for complements.

Consumer Theory and Indifference Curves
Consumers maximize utility subject to a budget constraint. The marginal rate of substitution MRS = $\frac{MU_X}{MU_Y}$. At equilibrium, MRS = $\frac{P_X}{P_Y}$.

Production and Costs
In the short run, firms face fixed and variable costs. Marginal cost (MC) is the addition to total cost of producing one more unit. The long-run average cost curve is U-shaped, reflecting economies of scale (declining), constant returns, and diseconomies of scale (rising).

Market Structures
- Perfect competition: price takers, P = MR = MC, zero economic profit in long run.
- Monopoly: P > MR, sets MR = MC, positive economic profit possible, deadweight loss exists.
- Monopolistic competition: differentiated products, zero economic profit in long run but excess capacity.
- Oligopoly: interdependence; may feature cartels or price leadership.

IV. Core Macroeconomic Framework Review

Macroeconomics examines the economy as a whole, including growth, inflation, unemployment, fiscal and monetary policy, and the balance of payments.

Aggregate Demand–Aggregate Supply (AD-AS) Model
The AD curve slopes downward due to wealth, interest-rate, and exchange-rate effects. Short-run aggregate supply (SRAS) slopes upward; long-run aggregate supply (LRAS) is vertical at potential output.
- Demand shock: rightward AD shift increases both price level and output.
- Supply shock: leftward SRAS shift produces stagflation (higher inflation and lower output).

Economic Growth and Production Functions
Per-capita GDP growth stems primarily from productivity gains, technological progress, and capital deepening.
Cobb-Douglas production function: $Y = A K^\alpha L^{1-\alpha}$.

Unemployment and Inflation
Natural unemployment rate = frictional + structural unemployment. The short-run Phillips curve shows a negative relationship between inflation and unemployment; the long-run Phillips curve is vertical at the natural rate.

Monetary and Fiscal Policy
Central banks influence money supply via open-market operations, reserve requirements, and the discount rate. Expansionary monetary policy lowers interest rates and stimulates investment and consumption. Fiscal policy affects aggregate demand through government spending and taxation. Crowding-out occurs when government borrowing raises interest rates and reduces private investment.

V. International Trade and Exchange Rates

Comparative Advantage
Countries should specialize in goods with the lowest opportunity cost. Trade improves welfare for both parties.

Balance of Payments
Current account (trade balance + services + income + transfers) + capital and financial account = 0 (ignoring statistical discrepancy).

Exchange Rate Determination
- Purchasing power parity (PPP): $S = \frac{P_{domestic}}{P_{foreign}}$
- Interest rate parity (IRP): forward premium or discount equals interest rate differential
- Asset market approach: higher real interest rates attract capital inflows and appreciate the currency.

Under fixed exchange rates, the central bank must intervene in the foreign exchange market; under floating rates, the exchange rate is market-determined.

Worked Cases

Case 1: Price Elasticity and Total Revenue

A good currently sells for $10 with quantity demanded of 200 units. Price rises to $12 and quantity falls to 160 units. Calculate price elasticity of demand and determine the effect on total revenue.

Solution:
$\% \Delta P = \frac{12-10}{10} \times 100\% = 20\%$
$\% \Delta Q = \frac{160-200}{200} \times 100\% = -20\%$
$E_d = \frac{-20\%}{20\%} = -1$ (unit elastic).
With unit elasticity, total revenue remains approximately unchanged. Original revenue = $10 \times 200 = 2,000$; new revenue = $12 \times 160 = 1,920$. (Midpoint formula yields elasticity very close to –1; minor difference is due to linear approximation.)

Case 2: Monopoly Profit Maximization

A monopolist faces demand $P = 100 - 2Q$ and constant marginal cost $MC = 20$. Calculate the profit-maximizing quantity, price, and economic profit (assume no fixed costs).

Solution:
$TR = (100-2Q)Q = 100Q - 2Q^2$
$MR = 100 - 4Q$
Set MR = MC: $100 - 4Q = 20 \Rightarrow Q = 20$
$P = 100 - 2(20) = 60$
Total revenue = $60 \times 20 = 1,200$; total cost = $20 \times 20 = 400$; economic profit = $800$.

Case 3: Expansionary Monetary Policy in an Open Economy

A country operates under floating exchange rates. The central bank conducts expansionary monetary policy by increasing money supply. Analyze the effects on domestic output, interest rates, and the currency using the IS-LM-BP or AD-AS framework.

Solution:
Increased money supply shifts LM rightward, lowering interest rates and causing capital outflows. The domestic currency depreciates, boosting net exports and shifting IS rightward. Result: domestic output rises, interest rates may return close to or slightly below the initial level, and the currency depreciates.

Traps

Key Formulas

• Price elasticity of demand: $E_d = \frac{\% \Delta Q_d}{\% \Delta P}$
• Monopoly marginal revenue: $MR = P\left(1 + \frac{1}{E_d}\right)$
• Profit-maximizing condition (all structures): $MR = MC$
• Approximate uncovered interest rate parity: forward premium ≈ domestic interest rate – foreign interest rate
• Money multiplier: $\frac{1}{\text{reserve ratio}}$
• Real interest rate = nominal interest rate – expected inflation
• Unemployment rate = $\frac{\text{unemployed}}{\text{labor force}} \times 100\%$
• Cobb-Douglas: $Y = A K^\alpha L^{1-\alpha}$

Practice Questions

Q1. If the price elasticity of demand for a good is –1.5 and price falls by 5%, quantity demanded will:
A. fall by 7.5%
B. rise by 7.5%
C. fall by 3.33%
D. rise by 3.33%

Q2. In a perfectly competitive market, a firm’s short-run supply curve is:
A. its AVC curve
B. its ATC curve
C. the portion of its MC curve above AVC
D. the portion of its MC curve above ATC

Q3. Which of the following is most likely to shift the long-run aggregate supply curve to the left?
A. Increased government transfer payments
B. A decline in the educational level of the workforce
C. An increase in the money supply
D. Technological progress

Q4. If the interest rate differential between two countries is 3%, according to uncovered interest rate parity the domestic currency is expected to:
A. appreciate by 3%
B. depreciate by 3%
C. appreciate by 6%
D. remain unchanged

Q5. In long-run equilibrium, a monopolistically competitive firm sets price relative to marginal cost such that:
A. P = MC
B. P > MC
C. P < MC
D. P = ATC = MC

Q6. If a central bank raises the required reserve ratio, the most likely immediate effect is:
A. an increase in the money multiplier
B. a decrease in the money supply
C. a decrease in interest rates
D. an increase in aggregate demand

Q7. A negative income elasticity of demand is most characteristic of:
A. luxury goods
B. normal goods
C. inferior goods
D. Giffen goods (price effect only)

Q8. In the AD-AS model, a negative supply shock will most likely cause:
A. lower price level and higher real output
B. higher price level and lower real output (stagflation)
C. higher price level and higher output
D. lower price level and lower output

Answers

Takeaways

• Elasticity signs carry precise economic meaning: price elasticity is usually negative; income elasticity sign distinguishes normal versus inferior goods.
• Perfect competition and monopolistic competition both yield zero long-run economic profit, yet monopoly and oligopoly can sustain positive profit.
• Monetary policy is more powerful under floating exchange rates; fiscal policy is more effective under fixed rates (Mundell-Fleming implication).
• Purchasing power parity focuses on inflation differentials while interest rate parity focuses on nominal interest differentials; both have important assumptions frequently tested.
• The AD-AS model is the primary framework for analyzing policy effects—demand and supply shocks produce distinctly different combinations of price and output changes.
• Comparative advantage, not absolute advantage, determines mutually beneficial trade patterns; this remains one of the most fundamental yet frequently misapplied principles in international economics.