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Percentages and interest

Percentages and interest for GCSE Computer Science Edexcel Higher: what it means, how to set the working out, and the questions it is asked in.
  • GCSE
  • Edexcel
  • Computer Science
  • Higher
  • Spec N19
  • 14 min read
  • 9 revision boxes

Introduction

2 boxes
3 min read

What is percentages and interest?

Listen to this box

Transcript

A short spoken summary of percentages and interest and where it is used.

A spoken walk-through of percentages and interest before you read the notes.
Read the units in the question before you start; a converted unit is the most common slip.
3 rows

The percentages and interest reference table

The specification wording is precise here, and the mark scheme follows that wording exactly.
The layout below is the one the mark scheme expects.

Diagram showing percentages and interest laid out step by step

The same idea drawn out, so the method is visible.
Term
Meaning
Example
Common slip
Marks
Row 1 column 1
Row 1 column 2
49=7\sqrt{49} = 7
Row 1 column 4
Row 1 column 5
Row 2 column 1
Row 2 column 2
49=7\sqrt{49} = 7
Row 2 column 4
Row 2 column 5
Row 3 column 1
Row 3 column 2
34×25\frac{3}{4} \times \frac{2}{5}
Row 3 column 4
Row 3 column 5
Row 4 column 1
Row 4 column 2
x2+5x+6=0x^2 + 5x + 6 = 0
Row 4 column 4
Row 4 column 5

Learning

5 boxes
5 steps

How to work with percentages and interest

Work through the method one line at a time and write down what changes at each step.
  1. Read the question and write down what is being asked for.
  2. Set out the working for percentages and interest in the order the method gives.
  3. Substitute the values and simplify.
Start from the definition and substitute the numbers the question gives you.
Simplify one line at a time: a2+b2=c2a^2 + b^2 = c^2.
Answer: 49=7\sqrt{49} = 7
3 rules

Key facts: Percentages and interest

Check the answer against an estimate before you move on, so a place-value slip is caught here.

  • Rule 1

    How percentages and interest behaves in the 1st of the cases the specification names.
    ≈160\approx 160

  • Rule 2

    How percentages and interest behaves in the 2nd of the cases the specification names.
    ≈160\approx 160

  • Rule 3

    How percentages and interest behaves in the 3rd of the cases the specification names.
    34×25\frac{3}{4} \times \frac{2}{5}
4 steps

How to work with percentages and interest

Read the units in the question before you start; a converted unit is the most common slip.
  1. Read the question and write down what is being asked for.
  2. Set out the working for percentages and interest in the order the method gives.
  3. Substitute the values and simplify.
  4. Check the answer against an estimate before writing it down.
Start from the definition and substitute the numbers the question gives you.
Simplify one line at a time: ≈160\approx 160.
Answer: a2+b2=c2a^2 + b^2 = c^2
2 rules

Key facts: Percentages and interest

The specification wording is precise here, and the mark scheme follows that wording exactly.

  • Rule 1

    How percentages and interest behaves in the 1st of the cases the specification names.
    ≈160\approx 160

  • Rule 2

    How percentages and interest behaves in the 2nd of the cases the specification names.
    49=7\sqrt{49} = 7

  • Rule 3

    How percentages and interest behaves in the 3rd of the cases the specification names.
    34×25\frac{3}{4} \times \frac{2}{5}
4 steps

How to work with percentages and interest

Work through the method one line at a time and write down what changes at each step.
The layout below is the one the mark scheme expects.

Diagram showing percentages and interest laid out step by step

The same idea drawn out, so the method is visible.
  1. Read the question and write down what is being asked for.
  2. Set out the working for percentages and interest in the order the method gives.
  3. Substitute the values and simplify.
Start from the definition and substitute the numbers the question gives you.
Simplify one line at a time: x2+5x+6=0x^2 + 5x + 6 = 0.
Answer: ×10\times 10 moves every digit one column left

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Examples

2 boxes
2 marks · worked

Worked example: percentages and interest

Practise the routine version until it is automatic, then move to the multi-step questions.
3 marks · worked

Practice question 9: 49=7\sqrt{49} = 7

Practise the routine version until it is automatic, then move to the multi-step questions.
The layout below is the one the mark scheme expects.

Diagram showing percentages and interest laid out step by step

The same idea drawn out, so the method is visible.
Worth knowing: 34×25\frac{3}{4} \times \frac{2}{5}.

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Common questions

How many marks is percentages and interest usually worth?
Between one and four, depending on how many steps the question asks for.
Is this on the GCSE Computer Science Edexcel Higher paper?
Yes — it sits in the Probability strand.