|Percentages will appear at some point during your GCSE maths exam. You will normally be asked to find a percentage of an amount and then either increase or decrease the amount by that percentage. You could also be asked to work out by what percentage an amount has changed.|
|a) A secondhand car was
purchased for £8000. After three years the car's value had
decreased by 35%
i) Find 35% of £8000
ii) Find the price of the car after three years.
b) A classic car was bought for £5000. Two years later it was sold in auction for £6500. What is the percentage increase in value?
i) We begin by finding 10% of £8000 by dividing by 10. So 10% = £800.
Now 5% is half of 10% so 5% = £400
So 35% = 10% + 10% + 10% + 5% = 800 + 800 + 800 + 400 = £2800
On a calculator paper to find a percentage of an amount you can just multiply by the decimal equivalent of 35% = 0.35.
So 8000 x 0.35 = 2800.
ii) The find the value of the car after three years subtract 35% from the original amount.
£8000 - £2800 = £5200
To find the percentage change we use the formulae:
% change = difference between values x 100%
So the car has gone up in value from £5000 to £6500. This is a difference of £1500.
So the percentage change = 1500 ÷ 5000 x 100 = 30%
Find 65% of £340
|Increase 80 kg by 20%
|An athlete improves his time for running a race
from 32 seconds to 28 seconds.
What is the percentage change in race time?
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