PAss Functional Skills

Compound measures

Compound measures for GCSE Combined Science AQA Foundation: what it means, how to set the working out, and the questions it is asked in.
  • GCSE
  • AQA
  • Combined Science
  • Foundation
  • Spec S20 · S12
  • 5 min read
  • 7 revision boxes

Introduction

2 boxes
3 min read

What is compound measures?

Listen to this box

Transcript

A short spoken summary of compound measures and where it is used.

A spoken walk-through of compound measures before you read the notes.
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 compound measures laid out step by step

The same idea drawn out, so the method is visible.
4 rows

The compound measures reference table

Check the answer against an estimate before you move on, so a place-value slip is caught here.
Worth knowing: 34×25\frac{3}{4} \times \frac{2}{5}.
Term
Meaning
Example
Common slip
Row 1 column 1
Row 1 column 2
×10\times 10 moves every digit one column left
Row 1 column 4
Row 2 column 1
Row 2 column 2
≈160\approx 160
Row 2 column 4

Learning

3 boxes
3 steps

How to work with compound measures

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 compound measures 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: ×10\times 10 moves every digit one column left.
Answer: x2+5x+6=0x^2 + 5x + 6 = 0
3 rules

Key facts: Compound measures

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

  • Rule 1

    How compound measures behaves in the 1st of the cases the specification names.
    ×10\times 10 moves every digit one column left

  • Rule 2

    How compound measures behaves in the 2nd of the cases the specification names.
    34×25\frac{3}{4} \times \frac{2}{5}

  • Rule 3

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

How to work with compound measures

Work through the method one line at a time and write down what changes at each step.
Worth knowing: 49=7\sqrt{49} = 7.
  1. Read the question and write down what is being asked for.
  2. Set out the working for compound measures 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: ≈160\approx 160.
Answer: x2+5x+6=0x^2 + 5x + 6 = 0

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Examples

2 boxes
1 marks · worked

Worked example: compound measures

The examiner marks the working, so a correct answer with no method still drops marks.
The layout below is the one the mark scheme expects.

Diagram showing compound measures laid out step by step

The same idea drawn out, so the method is visible.
3 marks · worked

Practice question 7: ≈160\approx 160

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 compound measures laid out step by step

The same idea drawn out, so the method is visible.

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Common questions

How many marks is compound measures usually worth?
Between one and four, depending on how many steps the question asks for.
Is this on the GCSE Combined Science AQA Foundation paper?
Yes — it sits in the Ecosystems strand.