1. Welcome
GCSE Maths

2. 1. A cake has a diameter of 20cm
1. A cake has a diameter of 20cm. What is the length of ribbon I need to go around 4 cakes? Answer to 3 significant figures

3. Learn the skill– Convert a fraction to a decimal
2 5
Means to divide
2 ÷ 5 = 0.4

4. Try the skill– Convert a fraction to a decimal
4 8
……………………………………………
7 35
……………………………………………
5 40
……………………………………………

5. Converting between fractions & percentages
4 8
4 ÷ 8 = 0.5 then × by 100
5 40 =

6. Match the Fractions and the Percentages
35%
1/50
120%
7/20
24%
4/5 2%
6/5
80%
6/25

7. Percentages

8. Without a calculator
Remember how to find the following amounts and you can then work out any percentage:
50% = divide by 2
25% = divide by 2 again
75%?
10% = divide by 10
20%?
5%?
15%?
1% = divide by 100

9. 180

10. Without a calculator 20% of 400 = 15% of 60 = 60% of 600 = 5% of 350 =

11. How do you find a percentage with a calculator?
What is 34% of 812? What is 27% of 540?

12. One number as a percentage of another Level 2
One number as a percentage of another = identified number total amount ×100
Example
23 as a percentage of ×100
Calculate the following:
a)13 as a percentage of b) 39 as a percentage of 75.
Billy scores 48 marks out of 80 in his test. The pass mark is 63%. Did he pass?

13. Percentage change/percentage difference
Percentage change is where we discover what percentage an amount has increased or decreased by.
Percentage Change=
Difference in amounts Original amount ×100

14. Difference in amounts Original amount ×100
Percentage Change=
Difference in amounts Original amount ×100
Original Amount: £100
Final Amount: £110
Original Amount: £250
Final Amount: £300
Original Amount: £75
Final Amount: £87.50

15. Example: Question A watch has a full price of £32.99
A shop advertises it for £28.99
Work out the percentage reduction in price. Give your answer to 1 decimal place.

16. Your turn A man’s jacket is reduced from £20 to £17
What is the percentage reduction?

17. Code breaker Apply skills to solve the written historical fact.

18. Welcome
GCSE Maths

20. Reverse Percentages

21. There is a 20% sale on in Topshop. The bag I want is now £60.
What was the original cost of my bag?
% of full cost 60
1 %
100 %
Original amount
÷ ?
× 100

22. In a sale, everything is reduced by 30%
In a sale, everything is reduced by 30%. If an armchair costs £175 in the sale, how much did it cost before the sale?
% of full cost
175
1 %
100%
÷ ?
× 100

23. A mouse increases its body weight by 15%
A mouse increases its body weight by 15%. If it now weighs 368g, what was the mouse’s original weight? %
368
1 %
100 %
Original amount
÷ ?
× 100

24. Exam style question In a sale, normal prices are reduced by 20%.
Andrew bought a saddle for his horse in the sale.
The sale price was £220.
Calculate the normal price of the saddle .

25. Exam style question In a sale, normal prices are reduced by 12%.
The sale price of a DVD player is was £242.
Work out the normal price of the DVD player. .

26. Quick revision of skills!!!
Percentages
17 marks available

27. Question 1

28. Question 2

29. Question 3
(3 marks)

30. Question 4

31. Question 5

32. Individual study
Developing skills