Money Calculations (OCR GCSE Maths)

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Money Calculations

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?

  • 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
    • $1.40 will be displayed as 1.4 on screen but would be pronounced '1 dollar, 40 cents'
    • This is particularly important when using a calculator
  • It is not always necessary to round to two decimal places
    • then rounding to the nearest dollar, 10 dollars or 100 dollars may be appropriate
    • If large numbers are involved – e.g. for the cost of a car
    • Use the information in the question to make a judgement
  • Some currencies have large numbers (due to exchange rates)
    • Due to the high numbers involved and the changing nature of exchange rates it would be accurate enough to say $100 is 8160 rupees
    • 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

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

Examiner Tip

  • Use the information given in the question to decide how to round your final answer
  • Check that your answer matches the currency in the question

Worked example

In his favourite UK fashion store, Thomas buys 4 t-shirts costing £8.50 each and 2 pairs of shorts costing £7.20 each.  On his way home Thomas fills his car up with 45 litres of petrol at a price of £1.579 per litre.

Find out how much Thomas spent in total on clothes and petrol.

Find the total cost of the t-shirts, shorts and petrol separately.
Use the figures as they are given, do not round any at this stage.
 

4 space cross times space 8.50 space equals space 34
2 space cross times space 7.20 space equals space 14.4
45 space cross times space 1.579 space equals space 71.055

Total (add) these amounts.

The currency is Great British Pounds (£) and values are relatively small so it makes sense to round the final answer to two decimal places.

Thomas spends a total of £119.46 on clothes and petrol.

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Paul

Author: Paul

Expertise: Maths

Paul has taught mathematics for 20 years and has been an examiner for Edexcel for over a decade. GCSE, A level, pure, mechanics, statistics, discrete – if it’s in a Maths exam, Paul will know about it. Paul is a passionate fan of clear and colourful notes with fascinating diagrams – one of the many reasons he is excited to be a member of the SME team.