Maths · 1 Number

1.15 Money

Before you start

Adding, subtracting, multiplying and dividing decimals, with and without a calculator.
Rounding to 2 decimal places and to 3 significant figures.
Finding a percentage of an amount, e.g. $20$ % of an amount is $0.2$ times it (1.12).
An exchange rate is a rate: the value of one unit of one currency in another (1.11).

Syllabus objectives covered (2)

Calculate with money.
Convert from one currency to another.

Part 1 of 7

Writing an amount of money

The dollar, the euro and the pound each split into $100$ smaller units: $100$ cents make one dollar, $100$ cents make one euro and $100$ pence make one pound. So an amount in dollars has two digits after the decimal point, and those two digits are the cents.
To change cents into dollars, divide by $100$ , because $100$ cents make one dollar. $345$ cents is $3.45. $8$ cents is $0.08, not $0.8: $0.8 is $80$ cents.
A calculator does not know it is working with money, and it drops a final zero. A display of $4.8$ in a money answer means $4.80, four dollars and eighty cents. Write it as $4.80: that is how an amount of money is written, and it shows you read the display correctly.
Use one unit, not both. Write $0.45 or $45$ cents, never $0.45 cents. Before you add or compare amounts, check that they are all in dollars or all in cents.
When an answer is not exact, round it to the nearest cent, which is 2 decimal places. Sharing a $50 bill equally between $3$ people gives $50 \div 3 = 16.666 \dots$ , so $16.67 each.
Round only the final amount. A price per unit, such as $0.168 for each unit of electricity, can have more than two decimal places, and you use it exactly as given. If you round part of the working to the cent and then multiply it, the final answer can drift by a few cents.

Part 2 of 7

Totals, change and how many you can buy

For a bill of several items, multiply the quantity by the price for each item, then add. Three notebooks at $2.35 and two pens at $0.89 cost $3 \times 2.35 + 2 \times 0.89 = 7.05 + 1.78 = 8.83$ , so $8.83.
Change is the amount handed over minus the total. From a $20 note: $20 - 8.83 = 11.17$ , so $11.17 change.
Without a calculator, count up from the total instead of subtracting. From $8.83 to $9.00 is $17$ cents. From $9.00 to $20.00 is $11. So the change is $11.17. Counting up avoids borrowing across the decimal point, which is where subtraction slips happen.
To find how many you can afford, divide the money by the price of one. Then round down, because you cannot buy part of a ticket and you cannot spend money you do not have. With $50 and tickets at $7.50: $50 \div 7.50 = 6.66 \dots$ , so $6$ tickets. Check the next number up: $7$ tickets cost $52.50, which is too much.
The money left over is the budget minus what the tickets cost: $50 - 6 \times 7.50 = 5$ , so $5.00 is left.
When you need enough of something, round up. You need $130$ paper plates and they come in packs of $24$ . $130 \div 24 = 5.41 \dots$ , but $5$ packs hold only $120$ plates, so you must buy $6$ packs. At $3.85 a pack that is $6 \times 3.85 = 23.10$ , so $23.10.
Read the question to decide which way to round. 'How many can she buy' rounds down. 'How many must she buy' rounds up. Rounding to the nearest whole number answers neither question.
An offer changes how many items you pay for, not the price of each one. With '3 for the price of 2' on drinks at $1.60, buying $7$ drinks gives $2$ full groups of $3$ , where you pay for $4$ , plus $1$ drink at full price. You pay for $5$ drinks: $5 \times 1.60 = 8$ , so $8.00 instead of $7 \times 1.60 = 11.20$ .

Part 3 of 7

Bills: a fixed charge plus a price per unit

Many bills have two parts. A fixed charge is paid whatever you use. A price per unit is paid for each unit you use. Electricity, water, phone contracts and taxi fares can all be charged like this.
$bill = fixed charge + number of units \times price per unit$
For electricity, a unit is one kilowatt-hour (kWh). The number of units used is the new meter reading minus the old one. From $45 218$ to $45 826$ is $45 826 - 45 218 = 608$ units.
A fixed charge can be an amount per day. Then multiply it by the number of days. At $0.32 per day for $31$ days the fixed charge is $31 \times 0.32 = 9.92$ . At $0.19 per unit the $608$ units cost $608 \times 0.19 = 115.52$ . The bill is $9.92 + 115.52 = 125.44$ , so $125.44.
A bill may give its prices in cents: $32$ cents per day, $19$ cents per unit. Change them to dollars (divide by $100$ ) before you combine them with anything in dollars.
To work back from a bill to the units used, undo the steps in reverse order: subtract the fixed charge first, then divide by the price per unit. A taxi charges $3.50 plus $1.20 per km. A fare of $27.50 leaves $27.50 - 3.50 = 24$ dollars for the distance, and $24 \div 1.20 = 20$ , so the journey is $20$ km.
Subtract first because the fixed charge is not paid per kilometre. Only the money left after the fixed charge is taken off paid for distance. Dividing the whole $27.50 by $1.20 treats the fixed charge as if it bought kilometres too.
To compare two plans, work out the cost of each one for the same amount of use, then compare the two costs. A plan with a fixed charge and a low price per unit can be dearer for light use and cheaper for heavy use, so the answer depends on the amount used.

Part 4 of 7

Paying in instalments, and earnings

Buying on instalments (on credit) means you pay a deposit now, then a number of equal payments over time. The cash price is what you pay if you pay the whole amount at once.
$total paid = deposit + number of payments \times payment$
A bike has a cash price of $480. On instalments it costs a deposit of $60 and $12$ monthly payments of $38.50. The total paid is $60 + 12 \times 38.50 = 60 + 462 = 522$ , so $522.
The extra cost of instalments is the total paid minus the cash price: $522 - 480 = 42$ , so $42. Keep the two steps separate in your working. The total and the extra cost are different answers, and a question may ask for either.
A deposit may be given as a percentage of the cash price. A $25$ % deposit on $480 is $0.25 \times 480 = 120$ , so $120. No formula is given for percentages, so you must know that $25$ % of an amount is $0.25$ times it.
Earnings can be given for different periods. A salary is an amount per year. To find the amount per month, divide by $12$ . To find the amount per week, divide by $52$ , the number of whole weeks in a year. A salary of $33 600 is $33 600 \div 12 = 2800$ , so $2800 per month.
To compare two jobs, put both amounts in the same period first. $2800 per month and $650 per week cannot be compared until both are per year (or both per week).

Part 5 of 7

Changing money: which way to go

An exchange rate tells you what one unit of one currency is worth in another. The rates in this lesson are made up for the questions. Real rates change from day to day, so in an exam you use exactly the rate the question gives.
Going from the currency that has the $1$ , multiply. At £1 = $1.27, £150 is $150 \times 1.27 = 190.50$ , so $190.50. Each pound is worth $1.27, so $150$ pounds is $150$ lots of $1.27.
Going to the currency that has the $1$ , divide. $254 is $254 \div 1.27 = 200$ , so £200. You are counting how many lots of $1.27 fit into $254.
Treat the rate as a unit: $1.27 per pound. Pounds × dollars per pound leaves dollars. Dollars ÷ dollars per pound leaves pounds. If the units do not cancel to the currency you want, you have the operation the wrong way round.
Then check the size. Here one pound buys more than one dollar, so you must get more dollars than the pounds you hand over. $190.50 for £150 passes the check. If you had got $150 \div 1.27 = 118.11 \dots$ , you divided when you should have multiplied.
To turn a rate round, divide $1$ by it. £1 = $1.27, so $1 is worth $1 \div 1.27 = 0.787 \dots$ pounds, which is £0.787 to 3 significant figures.
Do not convert with a rounded reverse rate. $254 \times 0.787 = 199.898$ gives £199.90, which is $10$ pence out. Dividing by the rate as given, $254 \div 1.27$ , gives exactly £200.
Give the final amount to 2 decimal places, the nearest cent or penny, unless the question asks for a different accuracy.

Part 6 of 7

Finding a rate, and changing through a third currency

If you know what someone handed over and what they received, you can find the rate. Sara changes £350 and receives €406. You want the rate as euros for one pound, so divide the euros by the pounds.
$\frac{406}{350} = 1.16$
So £1 = €1.16. The currency that gets the $1$ goes on the bottom of the division. For the rate the other way, one euro in pounds, divide the pounds by the euros: $350 \div 406 = 0.862 \dots$ , so €1 = £0.862 to 3 significant figures.
Some rates are large numbers. At $1 = $83.2$ rupees, $45 is $45 \times 83.2 = 3744$ rupees, and $5000$ rupees is $5000 \div 83.2 = 60.096 \dots$ dollars, so $60.10. The method does not change. Only the size check looks different: there are far more rupees than dollars.
Sometimes you are given two rates against a third currency, and you must go through it. With £1 = $1.25 and €1 = $1.08, change £200 into euros in two steps: pounds to dollars, then dollars to euros.
Step 1 goes from the currency with the $1$ (pounds), so multiply: $200 \times 1.25 = 250$ , which is $250. Step 2 goes to the currency with the $1$ (euros), so divide: $250 \div 1.08 = 231.48 \dots$ , which is €231.48.
Carry the full value of the middle amount into the second step. Here $250 is exact. If the middle amount had more decimal places, rounding it first could change the last digit of your answer.
You can also make one direct rate. £1 is worth $1.25 \div 1.08 = 1.157 \dots$ euros, and $200 \times 1.157 \dots = 231.48 \dots$ euros, the same answer. This is a good way to check a two-step conversion.

Part 7 of 7

Commission, comparing prices and changing money back

A bank or exchange office may charge commission, a fee for changing the money. When the commission is a percentage of the money you hand over, take it off first, then convert what is left.
Changing £500 at £1 = €1.15 with $2$ % commission: the commission is $0.02 \times 500 = 10$ , so £10. You convert $500 - 10 = 490$ pounds: $490 \times 1.15 = 563.50$ , so you receive €563.50.
A shorter route: after $2$ % commission you convert $98$ % of the money, so $0.98 \times 500 = 490$ pounds in one step.
To compare prices in two countries, put both prices in the same currency first. Shoes cost €84 abroad and £75 at home, and £1 = €1.15. $84 \div 1.15 = 73.04 \dots$ , so the shoes abroad cost £73.04. They are cheaper abroad by $75 - 73.043 \dots = 1.956 \dots$ pounds, which is £1.96.
Say which is cheaper and by how much, with the currency. 'The shoes are £1.96 cheaper abroad' answers the question. '£73.04' on its own does not.
Changing money back can use a different rate. A bank might change pounds into euros at £1 = €1.15 but change euros back into pounds at £1 = €1.21. £100 becomes €115, and €115 changed straight back gives $115 \div 1.21 = 95.04 \dots$ , so £95.04. The £4.96 difference is what the bank keeps. If a question gives two rates, use each one only in its own direction.

Worked examples

Example 1. Amara's electricity meter reads $38 264$ units at the start of a $91$ -day period and $39 015$ units at the end. She pays a fixed charge of $41.5$ cents per day and $23.8$ cents for each unit used. (a) Calculate her bill for the period, to the nearest cent. (b) For the next $90$ days her bill is $199.19. Calculate the number of units she used.

Show the working

Change both prices to dollars first, because the bill is in dollars: $41.5$ cents is $0.415 and $23.8$ cents is $0.238. Both have three decimal places, and you use them exactly.
(a) Units used: the new reading minus the old reading.
$39 015 - 38 264 = 751$
Cost of the units:
$751 \times 0.238 = 178.738$
Fixed charge for $91$ days:
$91 \times 0.415 = 37.765$
Add, and round only now: $178.738 + 37.765 = 216.503$ , so the bill is $216.50.
(b) Undo the bill in reverse order. The fixed charge for $90$ days is $90 \times 0.415 = 37.35$ . Take it off first.
$199.19 - 37.35 = 161.84$
That $161.84 paid for the units, at $0.238 each, so divide.
$161.84 \div 0.238 = 680$
Check: $680 \times 0.238 + 37.35 = 161.84 + 37.35 = 199.19$ . It matches the bill.

Answer: (a) $216.50 (b) $680$ units

Example 2. A laptop has a cash price of $849. On instalments, Diego pays a deposit of $20$ % of the cash price, then $12$ monthly payments of $61.25. (a) Calculate the total Diego pays on instalments. (b) Calculate how much more this is than the cash price.

Show the working

(a) The deposit is $20$ % of $849. No formula is given for this, so use $20$ % $= 0.2$ .
$0.2 \times 849 = 169.8$
So the deposit is $169.80, written with two decimal places.
The monthly payments:
$12 \times 61.25 = 735$
The total paid is the deposit plus the payments: $169.80 + 735 = 904.80$ , so $904.80.
(b) Extra cost = total paid − cash price.
$904.80 - 849 = 55.80$
Size check: paying in instalments costs more than paying cash here, so the answer to (b) must be positive. A negative answer means you subtracted the wrong way round or left out the deposit.

Answer: (a) $904.80 (b) $55.80

Example 3. Kenji changes $360 into Japanese yen and receives $54 000$ yen. (a) Find the exchange rate in the form $1 = $n$ yen. (b) Write the rate in the form 1 yen = $m$ dollars, correct to 3 significant figures. (c) At the end of his trip Kenji has $12 750$ yen left. He changes it back at the rate from (a). Calculate how many dollars he receives. (d) Headphones cost $26 400$ yen in Japan and $189 at home. Determine where they are cheaper, and by how many dollars.

Show the working

(a) You want the yen for one dollar, so the dollars go on the bottom.
$54 000 \div 360 = 150$
So $1 = $150$ yen. Size check: far more yen than dollars, and $150$ yen for each dollar fits.
(b) For one yen in dollars, turn the rate round: $1 \div 150 = 0.006666 \dots$ , so 1 yen = $0.00667 to 3 significant figures. Notice that 2 decimal places would give $0.01, which is half as much again as the true value. The question asks for 3 significant figures, and that keeps the accuracy.
(c) Yen to dollars goes to the currency with the $1$ in (a), so divide, using the exact rate from (a) rather than the rounded rate from (b).
$12 750 \div 150 = 85$
So Kenji receives $85.00.
(d) Put both prices in dollars: $26 400 \div 150 = 176$ , so the headphones cost $176 in Japan.
Compare: $189 - 176 = 13$ . Give both parts of the answer: where it is cheaper, and the difference with its currency.

Answer: (a) $1 = $150$ yen (b) 1 yen = $0.00667 (c) $85.00 (d) Cheaper in Japan, by $13

Example 4. Priya wants to change £600 into euros. Her bank gives only these two rates: £1 = $1.27 and €1 = $1.09. It also charges $1.5$ % commission on the pounds before it changes them. Calculate how many euros Priya receives, to the nearest cent.

Show the working

Plan the route first: take off the commission, change pounds to dollars, then change dollars to euros.
Commission: $1.5$ % of £600 is $0.015 \times 600 = 9$ , so £9. She has $600 - 9 = 591$ pounds to change.
Pounds to dollars. The rate starts from £1, so multiply.
$591 \times 1.27 = 750.57$
Dollars to euros. The rate starts from €1, and you are going to euros, so divide.
$750.57 \div 1.09 = 688.596 \dots$
To the nearest cent that is €688.60. Size check: one pound buys $1.27 and one euro costs $1.09, so a pound buys a little more than one euro. €688.60 for £591 fits.
Check with one direct rate: £1 is worth $1.27 \div 1.09 = 1.165 \dots$ euros, and $591 \times 1.165 \dots = 688.596 \dots$ , the same answer.

Answer: €688.60

Where people go wrong

Mistake: Reading a calculator display of $4.8$ in a money answer as $4.08, or writing it as $4.8.

Instead: $4.8$ dollars is $4.80: four dollars and eighty cents. Write money with two decimal places.

The calculator drops the final zero. The first digit after the point counts tens of cents, so $4.8$ is $80$ cents. $4.08 is only $8$ cents.

Mistake: Rounding to the nearest whole number when finding how many items a budget buys, e.g. $50 \div 7.50 = 6.66 \dots$ , so $7$ tickets.

Instead: Round down when the question asks how many you can buy: $6$ tickets. Round up when it asks how many you need.

$7$ tickets cost $52.50, which is more than the $50 available. The situation decides the direction of rounding, not the size of the decimal part.

Mistake: Using a price in cents and a price in dollars in the same calculation, e.g. adding a fixed charge of $41.5$ cents per day for $91$ days, worked out as $91 \times 41.5$ , to a cost of $178.74 for the units.

Instead: Change every amount to the same unit before you calculate: $41.5$ cents is $0.415, so the fixed charge is $91 \times 0.415 = 37.765$ dollars.

$100$ cents make one dollar, so an amount written in cents is a number $100$ times bigger than the same amount in dollars. Mixing them makes one part of the bill $100$ times too large.

Mistake: Working back from a bill by dividing first: dividing a taxi fare of $27.50 by $1.20 per km, then taking off the $3.50 fixed charge.

Instead: Subtract the fixed charge first, then divide what is left by the price per unit: $(27.50 - 3.50) \div 1.20 = 20$ km.

The fixed charge is not paid per kilometre. Only the money left after it is taken off paid for the distance.

Mistake: Dividing the wrong way when finding an exchange rate, e.g. £350 bought €406, so £1 = $350 \div 406 = 0.862 \dots$ euros.

Instead: The currency that gets the $1$ goes on the bottom. For £1 in euros, divide the euros by the pounds: $406 \div 350 = 1.16$ , so £1 = €1.16.

$350 \div 406$ is pounds per euro, the value of €1. A size check catches it: £350 bought more than $350$ euros, so one pound must buy more than one euro.

Check yourself

Write as an amount in dollars: (a) $7$ cents (b) a calculator display of $13.5$ for an answer in dollars.
Answer
(a) $0.07 (b) $13.50
Leon buys a book for $6.45 and a game for $8.79. He pays with a $20 note. Work out his change without a calculator.
Answer
Total $6.45 + 8.79 = 15.24$ . Count up: $15.24 to $16 is $76$ cents, and $16 to $20 is $4, so the change is $4.76.
Paper cups come in packs of $30$ and cost $2.60 a pack. Mia needs $145$ cups. Calculate the cost of the packs she must buy.
Answer
$145 \div 30 = 4.83 \dots$ , and $4$ packs hold only $120$ cups, so she needs $5$ packs. $5 \times 2.60 = 13$ , so $13.00.
A taxi charges $3.20 plus $1.45 per km. A fare is $24.95. Calculate the length of the journey.
Answer
Take off the fixed charge first: $24.95 - 3.20 = 21.75$ . Then $21.75 \div 1.45 = 15$ , so $15$ km.
A phone has a cash price of $299. On instalments it costs a deposit of $45 and $10$ payments of $27.80. How much more does it cost on instalments?
Answer
Total $45 + 10 \times 27.80 = 45 + 278 = 323$ , so $323. Extra cost $323 - 299 = 24$ , so $24.
The exchange rate is €1 = $1.12. Change $392 into euros.
Answer
Going to the currency with the $1$ , so divide: $392 \div 1.12 = 350$ , so €350.
Kofi changes £240 and receives €276. Find the exchange rate in the form £1 = € $n$ .
Answer
Euros for one pound, so divide by the pounds: $276 \div 240 = 1.15$ , so £1 = €1.15.
The exchange rate is $1 = £0.79. Find the value of £1 in dollars, correct to 3 significant figures.
Answer
$1 \div 0.79 = 1.2658 \dots$ , so £1 = $1.27 to 3 significant figures.

Exam questions

Try each part first. Open the mark scheme after you have written your answer.

Question 1. A water company offers two plans. Plan A has a fixed charge of $18.60 each month, plus $2.35 for each cubic metre (m³) of water used. Plan B has no fixed charge and costs $3.10 for each m³ of water used.

(a) Calculate the cost on Plan A for a month in which $14.2$ m³ of water is used. 2 marks

Mark scheme

M1 18.60 + 14.2 × 2.35 oe
A1 51.97 cao

(b) In another month on Plan A, the bill was $65.60. Calculate the amount of water used that month. 2 marks

Mark scheme

M1 (65.60 − 18.60) ÷ 2.35 oe
A1 20 (m³) cao

(c) A household expects to use $22$ m³ of water in a month. Determine which plan is cheaper for that month, and by how much. 3 marks

Mark scheme

M1 18.60 + 22 × 2.35 (= 70.30)
M1 22 × 3.10 (= 68.20)
A1 Plan B, cheaper by 2.10 dollars cao. Alternative method: M2 for 22 × (3.10 − 2.35) (= 16.50) compared with 18.60 oe

Question 2. Do not use a calculator in this question. A café sells sandwiches for $4.85 each and drinks for $1.90 each.

(a) Work out the cost of $3$ sandwiches and $4$ drinks. 2 marks No calculator

Mark scheme

M1 3 × 4.85 (= 14.55) or 4 × 1.90 (= 7.60) seen
A1 22.15 cao

(b) Work out the change from a $50 note for this order. 1 mark No calculator

Mark scheme

B1 27.85; FT 50 − their (a)

(c) A teacher has $60 to spend on sandwiches only. Work out the greatest number of sandwiches she can buy, and the money she has left. 3 marks No calculator

Mark scheme

M1 60 ÷ 4.85 attempted, or a trial such as 12 × 4.85 (= 58.20) or 13 × 4.85 (= 63.05)
A1 12 cao
B1 1.80; FT 60 − their whole number × 4.85, if positive

Question 3. Malik lives in the UK. Before a holiday in France he changes £420 into euros. The exchange rate is £1 = €1.15.

(a) Calculate the number of euros Malik receives. 1 mark

Mark scheme

B1 483 cao

(b) A jacket costs €69 in France. The same jacket costs £61.50 in the UK. Using the exchange rate above, determine where the jacket is cheaper, and by how much in pounds. 2 marks

Mark scheme

M1 69 ÷ 1.15 (= 60), or 61.50 × 1.15 (= 70.725) to compare in euros
A1 France, cheaper by £1.50 cao

(c) At the end of the holiday Malik changes his last €98.80 back into pounds. He receives £80. Calculate the exchange rate the bank used, in the form £1 = € $n$ . 2 marks

Mark scheme

M1 98.80 ÷ 80
A1 1.235 cao

(d) Explain why Malik would have received more pounds for his €98.80 if the bank had used the rate £1 = €1.15. 2 marks

Mark scheme

B1 98.80 ÷ 1.15 = 85.9(1…) seen, or the statement that each pound cost €1.235 instead of €1.15
B1 Conclusion: at €1.235 each pound costs more euros, so the same €98.80 buys fewer pounds (£80 rather than £85.91) oe

How this is examined

Working out a bill made of a fixed charge plus a price per unit, and working back from a bill to the units used: A bill question in two directions: find the bill for a given amount of use, then find the amount of use from a given bill For the bill: fixed charge + units × price per unit, with any prices in cents changed to dollars first. Going back: the fixed charge subtracted before dividing by the price per unit, e.g. $(65.60 - 18.60) \div 2.35$ . In each direction the method mark is for that expression and the accuracy mark is for the value it gives.
The total cost of buying on instalments, and how much more it is than the cash price: A Calculate part with a deposit (possibly given as a percentage of the cash price) and a number of equal payments, then a second step for the extra cost The deposit worked out (e.g. $0.2 \times 849 = 169.80$ ), the payments as number × payment, then deposit + payments for the total. The extra cost is a separate subtraction of the cash price from that total.
How many items a budget buys, and the money left over: A Work out part, which can be on the non-calculator paper, with a budget and the price of one item The budget divided by the price, or a trial such as $12 \times 4.85 = 58.20$ ; the whole number rounded down, with the next number up shown to cost too much; then budget − cost for the money left.
Comparing the price of the same item in two currencies: A Determine part after a conversion, asking where something is cheaper and by how much One price converted so that both are in the same currency (e.g. $69 \div 1.15 = 60$ ) for the method mark; then a statement naming where it is cheaper and the difference with its currency sign for the accuracy mark.
Changing money with a given rate in either direction, and finding a rate from what was handed over and received: Short Calculate parts: convert an amount, convert it back, or find the rate in the form £1 = € $n$ Multiply going from the currency with the 1, divide going to it. For a rate, the amount received divided by the amount handed over (e.g. $98.80 \div 80 = 1.235$ ), which gives the value of one unit of the currency handed over.
Writing a money answer to the cent: The final answer of any money part An exact amount written in full with two decimal places ($51.97, $1.80), and an amount that is not exact rounded to 2 decimal places only at the end, from unrounded working.

Words to know

Cent: One hundredth of a dollar or of a euro: $100$ cents make $1.
Change: The money given back when you pay more than the total. Change = amount handed over − total.
Fixed charge: An amount on a bill that is paid whatever you use, such as a charge per day or per month.
Unit (of electricity): One kilowatt-hour (kWh). Units used = new meter reading − old meter reading.
Cash price: The price when you pay the full amount at once.
Deposit: The first payment made when you buy on instalments. It may be a percentage of the cash price.
Instalments: Equal payments made over time to pay for something bought on credit.
Salary: Pay given as an amount per year. Divide by $12$ for a month, or by $52$ for a week.
Currency: The money system of a country or group of countries, e.g. dollars, euros, pounds.
Exchange rate: The value of one unit of one currency in another, e.g. £1 = €1.15.
Commission: A fee charged for changing money. It can be a fixed amount or a percentage of the money changed.

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