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Compound measures

Compound measures for GCSE Biology OCR: what it means, how to set the working out, and the questions it is asked in.
  • GCSE
  • OCR
  • Biology
  • Spec G9 · G6
  • 4 min read
  • 8 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.
The specification wording is precise here, and the mark scheme follows that wording exactly.
4 rows

The compound measures reference table

Read the units in the question before you start; a converted unit is the most common slip.
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.
Worth knowing: a2+b2=c2a^2 + b^2 = c^2.
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
≈160\approx 160
Row 2 column 4
Row 2 column 5

Learning

4 boxes
3 steps

How to work with compound measures

Check the answer against an estimate before you move on, so a place-value slip is caught here.
  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: a2+b2=c2a^2 + b^2 = c^2.
Answer: a2+b2=c2a^2 + b^2 = c^2
3 rules

Key facts: Compound measures

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.
Worth knowing: 34×25\frac{3}{4} \times \frac{2}{5}.

  • 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.
    ≈160\approx 160

  • Rule 3

    How compound measures 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 compound measures

The specification wording is precise here, and the mark scheme follows that wording exactly.
Worth knowing: ×10\times 10 moves every digit one column left.
  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
2 rules

Key facts: Compound measures

Read the units in the question before you start; a converted unit is the most common slip.
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.
Worth knowing: ≈160\approx 160.

  • Rule 1

    How compound measures behaves in the 1st of the cases the specification names.
    a2+b2=c2a^2 + b^2 = c^2

  • Rule 2

    How compound measures behaves in the 2nd of the cases the specification names.
    a2+b2=c2a^2 + b^2 = c^2

  • Rule 3

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

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Examples

2 boxes
2 marks · worked

Worked example: compound measures

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

Practice question 8: ≈160\approx 160

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

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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 Biology OCR paper?
Yes — it sits in the Ecosystems strand.