GCSE Secondary Maths Age 13-17 - Ratio, Proportion & Rates of Change: Percentages - Explained

The video tutorial explains how to calculate 15% of 80 without a calculator. It starts by finding 10% of 80, which is 8, and then calculates 5% by halving 10%, resulting in 4. Adding these two results gives 15% of 80, which is 12. The tutorial also discusses the marks allocation for the method and final answer.

What is the first step in calculating 15% of 80 without using a calculator?

• Find 20% of 80

• Find 10% of 80

• Find 5% of 80

• Find 50% of 80

How do you calculate 10% of a number?

• Add 10 to the number

• Multiply the number by 0.1

• Subtract 10 from the number

• Divide the number by 10

What is 10% of 80?

• 10

• 8

• 12

• 5

How do you find 5% of a number if you know 10% of it?

• Subtract 10% from the number

• Double the 10% value

• Add 10% to the number

• Take half of the 10% value

What is the final answer for 15% of 80?

• 10

• 16

• 14

• 12