Percentage Changes

Key Facts and Exam Tips

• A percentage change can be an increase or a decrease in a value.
• A discount means a reduction in price: that is, a decrease.
• A percentage decrease is subtracted from the original value.
• A percentage increase is added to the original value.

The formula

(percentage change) = ^(change) / _(original) x 100%

is used to calculate the percentage increase or decrease represented by a change in values.

The original value often appears in the exam question after the word 'from'.

Remember to divide by the original value and not by the value after the change has taken place.

If you are asked to give your answer to a number of significant figures or decimal places, you should do this or be prepared to lose marks. If the question involves money then you should normally round your answer to the nearest penny (2 decimal places), or to the nearest pound, as appropriate.

If you are asked to find an original price, size or quantity from values given after a percentage change, you need to think of the original as 100%. Given what percentage the new amount is, work back to find the original 100% value.