Find percentages and fractions of amounts

• Bronze: Calculate a percentage of an amount

• Silver: Calculate a fraction of an amount

• Gold: Use reasoning skills to compare fractions and percentages.

Percentages without a calculator

• To find a percentage of an amount we do the same calculation to the amount as we would do to get from 100% to our percentage.

• To get from 100% to 1% we would need to divide by 100, so we would divide the amount by 100.

• We always use multiply or divide.

Percentages without a calculator

What sum would we do to find 60%?

• As 60 is a multiple of 10, we can find 10% then multiply it by 6 to get 60%

What sum would we do to find 75%?

• For 75%, it is best to find 25% and multiply this by 3.

What sum would we do to find 5%?

• For 5%, it is best to find 10% and divide it by 2.

• Alternatively you could get to 5% by dividing 100% by 20

Percentages without a calculator

• We are now going to calculate some percentages without using a calculator.

• We will find the percentages using the strategies we looked at in the previous section.

Percentages without a calculator

A post office deals with 800 customers in a day. 70% of these buy stomps.

How many customers buy stamps?

A shop usually sells a bottle of bath gel for £2.60

The shop has a special offer on bath gel.

A woman is looking at her household bills throughout the year.

The total cost of electricity and supply for the fourth period is £120. 

The electricity company adds VAT to this total at a rate of 5% 

What is 5% of £120?

Fractions of an amount

Bob has £5, he donates 2/5 of it. How much does he have left?

Would you rather have...?

Would you rather have...?

Exit ticket

Complete the Century task set for this week. You must do this to get your mark.