DSE Economics | Balance of Payments and Exchange Rates Lesson Prep

DSE Economics | Balance of Payments and Exchange Rates Lesson Prep | From trade figures to depreciation

2026-11-04

Tutor lesson-prep guides · Secondary Economics

Students see a goods deficit of 400 billion and conclude the economy is in trouble, yet the same figures give a current account surplus once services are counted. This lesson uses a four-row table, then exchange rate conversion, then the 7.75 to 7.85 band that forces Hong Kong rates to follow the United States.

Objectives — Students can: (1) compute the current account from the goods, services, income and transfers lines and distinguish the trade balance from the current account balance; (2) convert a local price into a foreign price and judge how depreciation affects quantity, export revenue and domestic prices; (3) explain the Marshall-Lerner condition and why a linked rate removes monetary independence.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Law of demand	What happens to quantity demanded when price rises?	It falls, a movement along the curve
Elasticity	What does elastic demand mean?	Quantity changes by a larger percentage than price
GDP components	What are the four expenditure components?	Consumption, investment, government spending, net exports

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-8 min	Three-question check	Demand law, elasticity, GDP components	Answer orally
8-24 min	Four current account lines	Goods, services, income, transfers	Fill the table and total it
24-38 min	Exchange rate conversion	One good at 7.75, 7.80, 7.85	Compute three foreign prices
38-50 min	Does depreciation work	Elasticity sum and the J curve	Decide and justify
50-57 min	Timed practice	One balance sum, one conversion	Work alone
57-60 min	Exit check	Three checkpoints, one question each	Self-mark and circle slips

03 Teaching script (read it out)

Scene 1: The current account: four rows before one total

The current account has four rows. Goods exports 4500 and imports 4900 give a goods balance of -400; services exports 1200 and imports 500 give +700; net external income is -300; net transfers are +50. The four rows sum to +50, about 1.7 per cent of GDP. A headline goods deficit therefore does not settle the question: a large services surplus can reverse the conclusion entirely.

Require all four rows before any total. Marks are usually lost on the services line.

Scene 2: Exchange rate conversion: one good, three prices

A good priced at 780 Hong Kong dollars costs 100.00 US dollars at 7.80. If the dollar weakens to 7.85 the same good costs 99.36, cheaper for foreign buyers; at 7.75 it costs 100.65. The local price did not move, only the rate did, yet the foreign price and therefore the quantity change. Revenue is price times quantity, so the price fall must be more than offset by the quantity rise. With elasticities 0.4 plus 0.7 equal to 1.1, above one, depreciation improves the trade balance; below one it worsens it first, which is the J curve.

Insist on three steps: rate changes, foreign price changes, quantity changes. Revenue is the last step.

Scene 3: The linked rate: between 7.75 and 7.85

The strong-side guarantee is 7.75 and the weak-side guarantee is 7.85, a band of about 1.3 per cent. When demand for Hong Kong dollars pushes the rate to 7.75 the authority buys US dollars and sells Hong Kong dollars; when capital leaves and the rate reaches 7.85 it sells US dollars, buys Hong Kong dollars and drains the banking system balance, pushing local rates up. Local rates therefore cannot be set independently: US hikes widen the gap, capital leaves, the weak-side guarantee is triggered, and local rates follow. That loss of monetary independence is the price of a fixed rate.

Close with the trade-off: a stable rate buys away rate autonomy, which is the Hong Kong version of the impossible trinity.

04 Question types and worked steps

Type	Example	Steps	Answer
Balance calculation	Goods 4500/4900, services 1200/500, income -300, transfers +50	Net each row, then add	Current account +50
Conversion	A 780 dollar good, rate moves from 7.80 to 7.85	Divide the local price by the rate	99.36 US dollars
Depreciation effect	Elasticity sum 1.1, export volume up 8 per cent	Revenue is price times quantity	Revenue rises
Mechanism	US rates rise, what happens locally	Gap, capital flow, weak-side guarantee	Local rates follow up

Sanity check (teach this): The numbers must agree: the four rows sum to +50, about 1.7 per cent of GDP, the right order for a small open economy. The three converted prices 100.00, 99.36 and 100.65 differ by less than two per cent, exactly the size of the 1.3 per cent band. Anyone claiming depreciation raises export revenue automatically must answer how far price fell against how far quantity rose.

05 Independent practice (3 questions)

Question	Answer	What to watch
Current account: goods -600, services +450, income -200, transfers +30	-320	Signs on every row
Rate moves from 7.80 to 7.50, what happens to a 900 dollar good	From 115.38 to 120.00 US dollars	Direction and value
Why depreciation may not improve the trade balance at once	Elasticity sum below one, worse before better	Mentions the J curve

06 Common mistakes and what to say

Mistake	Student writes	Say this
Treating the trade balance as the current account	Says a goods deficit means a current account deficit	Three more rows exist, and the services surplus is large.
Assuming depreciation always raises export revenue	Counts the quantity gain only	Compare the percentage price fall with the quantity rise.
Reversing the direction of depreciation	Calls 7.85 an appreciation	A larger number means more local dollars per US dollar, so the local currency is weaker.
Thinking local rates are a free policy tool	Says the authority can cut at will	The weak-side guarantee forces a defence, so rates track the United States.

07 Homework (paper, section and question numbers)

Economics chapter index — All chapters
Economics practice papers — International trade: current account and exchange rate questions

08 Exit check (last 5 minutes)

Question	Answer	Decision
Current account	Goods -400, services +700, income -300, transfers +50	Cannot total: reteach the four rows
Direction	Is 7.85 stronger or weaker than 7.80	Says stronger: return to the definition
Mechanism	Why local rates follow US hikes	Only says they follow: add the guarantee and the balance

09 Tutor FAQ

Why does the services surplus matter so much here?

Tourism, transport, finance and professional services are major exports, and their surplus often offsets the goods deficit, so goods alone mislead.

Can the linked rate be changed?

In principle yes, but the credibility cost is severe, so in practice it is treated as a commitment rather than a policy instrument.

Must students memorise the J curve numbers?

No. The mechanism and the elasticity condition matter; the exact figures do not.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.