1 of 27

Mathematics GCSE Revision Session

Mrs Claire Dixon

BSc (Hons), PGCE, MEd

​

Teacher

Pentrehafod School, Swansea

Percentages

(Non-Calculator)

2 of 27

Mathematics GCSE Revision Session

Session 1: Solving linear equations

​

Session 2: Solving simultaneous equations

​

Session 3: Percentages (Non-Calculator)

​

Session 4: Percentages (Calculator)

​

Session 5 (Live Session): Recap of sessions 1 – 4

3 of 27

4 of 27

Starter

  1. Convert the following decimals to percentages:
  2. 0.25
  3. 0.3
  4. 0.87
  5. 0.06

​

  1. Calculate:
  2. 6 ÷ 10
  3. 12 ÷ 60
  4. 100 ÷ 120

5 of 27

Finding a percentage of a quantity

Success Criteria:

​

  • The method for finding 50% is to divide by 2.

​

  • The method for finding 25% is to divide by 4.

​

  • The method for finding 10% is to divide by 10.

​

  • The method for finding 1% is to divide by 100.

6 of 27

Task

Find:

  1. 50% of 90

​

  • 25% of 1200

​

  • 10% of 80

​

  • 1% of 150

Finding a percentage of a quantity

7 of 27

Finding a percentage of a quantity

Success Criteria:

​

  • The method for finding 20% is to ÷ 10, then x2.

​

  • The method for finding 30% is to ÷ 10, then x3.

​

  • The method for finding 40% is to ÷ 10, then x4.

​

etc

8 of 27

Task

Find:

  1. 30% of 40

​

​

  • 60% of 2500

​

​

  • 40% of 6

​

Finding a percentage of a quantity

9 of 27

Finding a percentage of a quantity

Success Criteria:

​

  • The method for finding 2% is to ÷ 100, then x2.

​

  • The method for finding 3% is to ÷ 100, then x3.

​

  • The method for finding 4% is to ÷ 100, then x4.

​

etc

10 of 27

Task

Find:

  1. 5% of 90

​

​

  • 4% of 3600

​

​

  • 7% of 4

​

Finding a percentage of a quantity

11 of 27

Task

A pair of trainers are in a sale.

They were originally £60.

They have 15% off.

How much money do I save?

​

Finding a percentage of a quantity

12 of 27

Task

A pair of designer sunglasses are in a sale.

They were originally £150.

They have 24% off.

How much money do I save?

​

Finding a percentage of a quantity

13 of 27

Expressing one number as a percentage of another

Success Criteria:

  • Write the numbers as a fraction.
  • Convert the fraction so it has a denominator of 100

OR work out the numerator divided by the denominator.

  • Multiply by 100

14 of 27

Expressing one number as a percentage of another

Example:

​

Express 15 as a percentage of 20

15 of 27

Expressing one number as a percentage of another

Task

Express the following as a percentage of the other:

  1. 83 out of 100
  2. 24 out of 50
  3. 9 out of 25
  4. 7 out of 20
  5. 6 out of 10
  6. 24 out of 60

16 of 27

Expressing one number as a percentage of another

Example:

In a class of 32 students, 12 of them are boys.

What percentage of the class are boys?

17 of 27

Expressing one number as a percentage of another

Task

1. George scored 12 out of 15 in his Geography test.

What was his percentage score?

​

​

2. 14 out of 21 apples in a sack were mouldy.

What percentage of the apples were NOT mouldy?

18 of 27

Expressing one number as a percentage of another

Example (Different Units):

Express 75cm as a percentage of 2.5m

19 of 27

Expressing one number as a percentage of another

Task (Different Units):

Express 45 minutes as a percentage of 2 hours

20 of 27

Calculating percentage changes (increase and decrease)

 

21 of 27

Example

A television originally costing £500 is reduced by £30.

Calculate the reduction as a percentage of the original price.

Calculating percentage changes (increase and decrease)

22 of 27

Task

Jane earns £8 per hour. She receives a pay increase of 50p per hour.

Calculate her pay increase as a percentage of the original price.

Calculating percentage changes (increase and decrease)

23 of 27

Key words:

​

Appreciation – when the value of an item increases.

​

Depreciation – when the value of an item decreases.

Repeated proportional changes: appreciation and depreciation

Success Criteria:

  • Calculate the percentage of the quantity.
  • Either add (appreciation) or subtract (depreciation) from the starting amount.

24 of 27

Repeated proportional changes: appreciation and depreciation

Example

Ben puts £300 in the bank at 5% compound interest per year.

How much money will he have in the bank after 2 years?

25 of 27

Repeated proportional changes: appreciation and depreciation

Example

Sally buys a car for £6000. The car depreciates by 10% per year.

How much is the car worth after 3 years?

26 of 27

Percentages Plenary

Which of these is the odd one out?

40% of 900

90% of 400

60% of 850

25% of 1440

Explain your answer

27 of 27

Mathematics GCSE Revision Session

Session 1: Solving linear equations

​

Session 2: Solving simultaneous equations

​

Session 3: Percentages (Non-Calculator)

​

Session 4: Percentages (Calculator)

​

Session 5 (Live Session): Recap of sessions 1 – 4