Money Calculations (Cambridge O Level Maths)

Many parts of the course can use questions involving money.
Fractions, percentages, simple and compound interest, depreciation are just a few.
The currency and size of the numbers involved in money calculations will dictate how you should round your final answers

What currencies can be used?

• These are international exams so many different currencies are used
• The most commonly used currencies are
• US Dollars ($ or USD)
• Great British Pounds (£ or GBP)
• Euros (€ or Euros)
• It is possible to see other currencies used, with or without their symbols

How should I round my answer in a money calculation?

• Many currencies will be rounded to two decimal places
• Dollars, pounds and euros should all be used to two decimal places
• When rounding, always write down both decimal places, even if the second is zero
• This is particularly important when using a calculator
• $1.40 will be displayed as 1.4 on screen but would be pronounced '1 dollar, 40 cents'
• It is not always necessary to round to two decimal places
• If large numbers are involved – e.g. for the cost of a car
• then rounding to the nearest dollar, 10 dollars or 100 dollars may be appropriate
• Use the information in the question to make a judgement
• Some currencies have large numbers (due to exchange rates)
• These are usually rounded to the nearest whole number
• E.g.  $10 is 816.38 Indian Rupees making $100  the same as 8163.80 rupees
• Due to the high numbers involved and the changing nature of exchange rates it would be accurate enough to say $100 is 8160 rupees

What should I do when money calculations involve more than two decimal places?

• In some contexts money facts may be given to more than two decimal places
• Common examples of this include exchange rates and the cost of gas or electricity
  • E.g. One litre of petrol in the UK costs an average price of £1.579
• In such cases you should use all of the decimal places given in your working and only round (to two decimal places or whatever is appropriate) for your final answer

What will I be asked to do in money calculations?

• Questions will not use words like add, subtract, multiply so think carefully about what you need to do
  • Words like total or sum will mean to add up
  • Difference – or increase/decrease in costs - will involve subtracting
  • Changing from one currency to another (exchange rates) will involve multiplying or dividing
• Working out the total cost of an energy bill may involve a combination of these