year 8 maths

242 Chapter 4 Fractions, decimals, percentages and financial mathematics
4H Decreasing and increasing by a percentage
Percentages are regularly used when dealing with money. Here are some examples.
• Decreasing an amount by a percentage (Discount)
All items in the store are reduced by 30% for the three-day sale.
The value of the car is depreciating at a rate of 18% per annum.
• Increasing an amount by a percentage (Mark-up)
A retail shop marks up items by 25% of the wholesale price.
The professional footballer’s new contract was increased by 40% .
When dealing with questions involving money, you generally round your answers to the nearest cent. Do
this by rounding, correct to two decimal places. For example: $356.4781 rounds to $356.48 (suitable if
paying by credit card).
As our smallest coin is the 5 cent coin, on many occasions it will be appropriate to round your answer to
the nearest 5 cents. For example: $71.12 rounds to $71.10 (suitable if paying by cash).
Let’s start: Original value ± % change = new value
The table below consists of three columns: the original value of an item, the percentage change that
occurs and the new value of the item. However, the data in each of the columns have been mixed up. Your
challenge is to rearrange the data in the three columns so that each row is correct.
This is an example of a correct row.
Original value Percentage change New value
$ 65.00 Increase by 10% $71.50
Rearrange the values in each column in this table so that each row is correct.
Original value Percentage change New value
$ 102.00 Increase by 10% $73.50
$80.00 Increase by 5% $70.40
$58.00 Decreased by 2% $76.50
$64.00 Decrease by 25% $78.40
$70.00 Increase by 30% $73.80
$82.00 Decrease by 10% $75.40
Cambridge Maths NSW
Stage 4 Year 8 Second edition
ISBN 978-1-108-46627-1 © Palmer et al. 2018
Cambridge University Press
Photocopying is restricted under law and this material must not be transferred to another party.