Welcome GCSE Maths

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

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

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

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

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

Percentages

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

180

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

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

One number as a percentage of another One number as a percentage of another = identified number total amount ×100 Example 23 as a percentage of 25 23 25 ×100 Calculate the following: a)13 as a percentage of 20 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?

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

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

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.

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

Break time

Reverse Percentages

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

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

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

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 .

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. .

Quick revision of skills!!! Percentages 17 marks available

Question 1

Question 2

Question 3 (3 marks)

Question 4

Question 5

Individual study Developing skills