Why do I keep getting the wrong answer when tackling percentage change questions?

Percentage change isn't always as simple as you think. Whilst taking into consideration if it is a percentage increase or decrease, you also need to consider whether you're calculating a result before or after the percentage change has taken place. 

For example, are you working out the value of a £13500 car after a 15% depreciation, or are you working out the original value of a £800 sofa before it was in a 30% off sale? There are some tips that can be learnt to ensure you never get a percentage change question wrong ever again.