Percentages

Objective

To calculate percentage increase and decrease.

Two methods how to increase a percentage

Method 1 – Find the increase and add it to the original amount

Method 2 – Using a multiplier

Percentage Increase

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

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…

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%

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

Percentage Decrease

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)

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…

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

Question Practice

Exam style Questions

Chapter 5 – Page 142

Exercise 5E

Q 8

Exercise 5F

Q 10

Overview

What have we learnt today?

Are we confident in answering questions on this part of the topic?

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

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