1. Objective To calculate percentage increase and decrease.
Percentages
Objective
To calculate percentage increase and decrease.

2. Percentage Increase Two methods how to increase a percentage
Method 1 – Find the increase and add it to the original amount
Method 2 – Using a multiplier

3. Method 1 Example: Increase £8 by 5% Find 5% of £8: 5 x 800p = 40p 100
Then add 40p to the original amount £8.40

4. Method 2 Example: Increase £8.50 by 7%
A 7% increase is a multiplier of 1.07
Therefore £8.50 x 1.07 = £9.10
Straightforward – use calculator method, or find 10% 1st then 1% etc…

5. Examples to complete
Bonus paid on salary of 3%, salary £1,200, what is the total salary?
An item costs £6.50 without VAT at 17.5%, what is the total cost?
Increase £50 by 60%
House Price Increase – 12%, 15%

6. Percentage Decrease Two methods how to decrease a percentage
Method 1 – Find the decrease and take it away from the original amount
Method 2 – Using a multiplier

7. Method 1 Example: Decrease £8 by 7% Find 7% of £8: 7 x 800p = 56p 100
Then take 56p off the original amount £7.44
(Without a calculator)

8. Method 2 Example: Decrease £8.50 by 7%
A 7% decrease is a multiplier of 0.93
Therefore £8.50 x 0.93 = £7.90
Straightforward – use calculator method, or find 10% 1st then 1% etc…

9. Examples to complete
Car valued at £13,500 when new, it lost 22% depreciation in the first year. What is it’s value?
Petrol Costs 81.9p per litre. What does it cost after a 2.4% decrease?
A scooter costs £24, but is reduced in a sale by 20%, what is the sale price?
House Decrease

10. Question Practice Exam style Questions Chapter 5 – Page 142
Exercise 5E
Q 8
Exercise 5F
Q 10

11. Overview What have we learnt today?
Are we confident in answering questions on this part of the topic?

13. What if the question doesn’t give the % Decrease?
Example - I achieved 66% in the first test and 64% in the second, what is the percentage increase?
Percentage Decrease = actual decrease x 100%
initial value
% decrease = 2 x 100% = 3% 66

14. What if the question doesn’t give the % Increase?
Example - I achieved 54% in the first test and 72% in the second, what is the percentage increase?
Percentage Increase = actual increase x 100%
initial value
% increase = 18 x 100% = 33% 54