2021/22 S3 Ex.2A Percentage

2021/22 S3 Ex.2 Percentage

by LHK

​Do you still remember Percentage you have learnt in S1?

Calculating % Amounts WITH a calculator (e.g. 24% of 440)

• Change the % to a decimal by dividing by 100 (just put 0. in front of the % number)

• For example, 17% (0.17)  86% (0.86)  5% (0.05)   41% (0.41)  etc

• So if we want to find 24% of 440, we change 24% to 0.24

• Then we multiply 0.24 by 440 = 105.6

• 24% of 440 is 105.6

Open Ended

What is 17% of 850?

Open Ended

What is 89% of 442?

Calculating % Amounts WITH a calculator (e.g. what is 33/60 as a percentage?)

Open Ended

What is 18/90 as a Percentage?

Open Ended

What is 150/400 as a Percentage?

Open Ended

What is 2/19 as a Percentage? Round your answer to 1 decimal place

Calculating Percentage Increases (e.g. you earn £22k, what is your new salary after a 1% pay rise?)

• Add the % increase to 100% and change to a decimal​

• 1% + 100% = 101%
  

• 101% as a decimal is 1.01

• Multiply 1.01 by £22,000  = £22,220

Open Ended

A TV that costs £270 has gone up in price by 35%, what is the new price?

Open Ended

Bob earns £450 per week and gets a pay rise of 2%; what is his new weekly pay?

Calculating Percentage Decreases (e.g. you earn £22k per year and get a 2% decrease)

• Take away the % decrease from 100% and change to a decimal​

• 100% - 2% = 98%
  

• 98% as a decimal is 0.98

• £22,000 x 0.98 = £21,560

Open Ended

A TV that costs £270 is reduced by 12%; what is the new price?

Open Ended

Bob earns £450 per week and gets a 3% pay cut; what is his new weekly wage?

Calculating Amount Changes as Percentages (e.g. a bag of apples has gone up from £1.25 to £1.30)

• Divide the increase by the original amount

• 0.05 ÷ 1.25 = 0.04
  

• Multiply by 100 (answer will be % increase)

• 0.04 x 100 = 4%

Open Ended

A car has gone up in price from £8000 to £8700; what % increase is this?

Open Ended

A holiday has gone up in price from £5000 to £5320; what % increase is this?

Calculating Amount Changes as Percentages (e.g. a bag of apples has gone down in price from £1.50 to £1.20)

• Divide the decrease by the original amount

• 0.30 ÷ 1.50 = 0.2
  

• Multiply by 100 (answer will be % decrease)

• 0.2 x 100 = 20%

Open Ended

A car that costs £8000 has been reduced to £7100; what % decrease is this?

Open Ended

A holiday has been reduced in price from £5000 to £3850; what % decrease is this?

Calculating Original amounts after changes have been made (e.g. an antique vase increases in value by 15% and is now worth £3,450; what was it worth originally?)

• Add the % increase to 100% and change to a decimal

• 15% + 100% = 115%
  

• 115% as a decimal = 1.15
  

• Divide the amount by the decimal

• £3450 ÷ 1.15 = £3000

Open Ended

Bob sold his car for £7500 which is a 20% profit; what did he originally pay for it?

Calculating Original amounts after changes have been made (e.g. If I’ve paid off 45% of my loan and now owe £1,980, how much did I owe originally?)

• Subtract (take away) the % decrease from 100% and change to a decimal

• 100% - 45% = 55%
  

• 55% as a decimal is 0.55
  

• Divide the amount by the decimal

• £1980 ÷ 0.55 = £3600

Open Ended

A car now costs £4500 after a 20% discount; what did it cost originally?