Currency Conversions
Change money from one currency to another with an exchange rate, go through a middle currency, find a rate, and compare prices in two countries.
In the exam for Cambridge IGCSE Maths 0580, Edexcel IGCSE Maths 4MA1, Cambridge O Level Maths 4024 · 68 real past-paper questions below
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What an Exchange Rate Means
An exchange rate tells you how much of one currency you get for one unit of another. In this lesson .
| Pounds | Euros |
| £1 | €1.16 |
| £10 | €11.60 |
| £100 | €116 |
Textbooks write the rule as a formula:
Formula
The rate is how much of the new currency one unit of your money buys (here 1.16 euros for each £1). Going the other way, you divide: amount you change = amount you get ÷ rate.
Rule
The side with the 1 is where you start. To go from that side, multiply by the rate. To come back, divide.
Multiply One Way, Divide Back
The 1 or 2-mark question: "Change £250 to euros", then "Change €348 to pounds". Each pound is worth 1.16 euros.
Worked example
- 1
— The question. Pounds are the side with the 1 (£1 = €1.16), so we start from that side.
- 2
— Each pound gives 1.16 euros, so 250 pounds give 250 lots of 1.16. Multiply.
- 3
— Check the size: one pound buys more than one euro, so the euro number should be the bigger one. It is.
- 4
— Now go the other way, from euros back to the side with the 1.
- 5
— Every 1.16 euros makes one pound, so count how many 1.16s fit in 348. Divide.
- 6
— Check by multiplying back. It gives the 348 euros we started with, so £300 is right.
Common mistake
Multiplying both ways. Check your answer: one pound buys more than one euro, so the euro number must be the bigger one.
Which Is Cheaper? Same Currency First
The 3 or 4-mark question: a jacket costs €87 in Paris and £70 in London. Where is it cheaper, and by how much?
Worked example
- 1
— The prices are in different currencies, so they cannot be compared yet. Change one so both are in pounds.
- 2
— Euros back to pounds, so divide by the rate. Paris costs £75.
- 3
— London is already in pounds, so it stays as it is.
- 4
— Both prices are now in pounds, so subtract the smaller from the bigger to find the difference.
- 5
— London has the smaller price. The question asks where and by how much, so give both, with the £ sign.
Common mistake
Comparing 87 with 70 straight away. They are different money, so the numbers mean nothing until both are in one currency.
Through a Middle Currency
The 3-mark question gives rates against pounds only, then asks you to change euros to another currency, such as AED (UAE dirhams). Go through pounds.
Use and . Change 580 euros to AED.
Worked example
- 1
— No rate links euros and AED directly, but both are given against pounds. So go through pounds.
- 2
— Euros back to pounds: the 1 is on the pounds side, so divide.
- 3
— Pounds out to AED: £1 = 4.6 AED starts from pounds, so multiply the £500 from the line before.
Key idea
Two rates means two steps. Write the middle amount down; it is worth a mark on its own.
Key idea
Given the end amount and asked for the start? Run the same steps backwards and swap each × for ÷. From 2300 AED: 2300 ÷ 4.6 = £500, then 500 × 1.16 = 580 euros.
Find the Rate, Then Use It
The 3-mark question: a bag costs £40 or 46 CHF (Swiss francs). A coat costs £60. What is the coat in CHF?
Worked example
- 1
— The same bag is £40 or 46 CHF. Divide the CHF by the pounds to get the rate: CHF for one pound.
- 2
— Write the rate with the 1 on the pounds side, so you can see which way to go.
- 3
— The coat is in pounds, the side with the 1, so multiply by the rate.
A harder 4-mark question gives two rates and asks which is better. Bank A: £1 = 1.16 euros. Bank B: 1 euro = £0.85. Change £500 at each.
Worked example
- 1
— Bank A has the 1 on the pounds side, so multiply.
- 2
— Bank B has the 1 on the euros side: each euro costs £0.85. Count how many 0.85s fit in 500, so divide.
- 3
— Money uses 2 decimal places, so round to the nearest cent.
- 4
— Subtract to compare. Bank B gives 8.24 euros more, so Bank B is the better deal.
Common mistake
Dividing the wrong way round to find the rate. The rate is how many of the other currency for one pound, so divide by the pounds.
Key idea
Some tables give the amount for 100, such as $100 = 85 euros. Divide by 100 first to get the rate for 1: $1 = 0.85 euros.
Rate Between Two Currencies
Some questions give two rates against one currency and ask for the rate between the other two. Divide one rate by the other.
When 1 unit of a middle currency = units of A, and the same 1 unit = units of B:
Formula
and are the two rates you are given. The one for the currency you want on top is b.
Worked example
- 1
— Both rates start from £1, so 1.16 euros and 4.6 AED are worth the same.
- 2
— Write them equal to each other, because each is worth exactly £1.
- 3
— We want 1 euro, so divide both sides by 1.16.
- 4
— Work it out. Keep the full number for any later step; round only the final answer.
- 5
— Check with the Through a Middle Currency card: 580 euros gave 2300 AED there too.
Common mistake
Working out 1.16 ÷ 4.6 = 0.25 instead. Ask: one AED is worth less than one euro, so 1 euro must buy more than 1 AED. The answer has to be bigger than 1.
Spend, Then Change Back
A common 3-mark question: change money, spend some abroad, then change what is left back. Stay in the foreign currency until the last step.
£1 = 1.16 euros. Lina changes £400 to euros, spends 350 euros, and changes the rest back to pounds.
Worked example
- 1
— Pounds to euros: pounds have the 1, so multiply. This is the money she takes.
- 2
— She spends 350 euros. Both numbers are in euros, so subtract to find what is left.
- 3
— Change only the euros left back to pounds. Euros back to pounds, so divide.
- 4
— Money uses 2 decimal places, so round to the nearest penny.
Key idea
Show every line. Writing 464 and 114 earns marks for working, even if a later line goes wrong. If the rate on the way back is different, use the new rate for the last step only.
Common mistake
Taking 350 from £400. You cannot subtract euros from pounds; change to euros first, then subtract.
Rounding Money Answers
Exams often say "to the nearest cent" or "to 2 decimal places". Some say the bank only gives notes. Here is how to round each time.
Rule
Nearest cent or penny means 2 decimal places. Nearest dollar, euro or rupee means a whole number. Write the full calculator number first, then round.
£1 = 1.16 euros. Sam changes £230, but the bank only gives euros in €10 notes. How many euros does he get, and what is his change in pounds?
Worked example
- 1
— Pounds to euros: multiply. This is the most he could get.
- 2
— The bank only gives €10 notes, so round down to a multiple of 10. €270 would cost more than £230.
- 3
— Find what the €260 costs in pounds: euros back to pounds, so divide.
- 4
— Take that cost from the £230 he brought. What is left comes back as change.
- 5
— Round to the nearest penny, 2 decimal places, as the very last move.
Key idea
Write the full calculator number before you round. There is often a mark just for rounding it correctly.
Which Method? Read the Question
Find the rate, then find which side has the 1.
| You see | You do |
| Change from the side with the 1 | multiply by the rate |
| Change to the side with the 1 | divide by the rate |
| Where is it cheaper? | same currency, then subtract |
| Two rates, neither fits | go through the middle currency |
| Asked for the rate between those two | divide one rate by the other |
| Two prices for one thing | divide to find the rate |
| Spend some, change the rest back | subtract in that currency, then convert |
| Nearest cent, or notes only | full number first, then round |
| A straight line graph of the rate | Conversion Graphs |
Key idea
Always check the size of your answer. The currency worth less per unit should have the bigger number.
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