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Tree diagrams

Tree diagrams for A Level Economics OCR: what it means, how to set the working out, and the questions it is asked in.
  • A Level
  • OCR
  • Economics
  • Spec P8 · P14 · P13
  • 9 min read
  • 6 revision boxes

Introduction

2 boxes
4 min read

What is tree diagrams?

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Transcript

A short spoken summary of tree diagrams and where it is used.

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

The same idea drawn out, so the method is visible.
Worth knowing: ≈160\approx 160.
2 rows

The tree diagrams reference table

Sketch the shape even when the question does not ask for one — it makes the next step obvious.
The layout below is the one the mark scheme expects.

Diagram showing tree diagrams 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
≈160\approx 160
Row 1 column 4
Row 1 column 5
Row 2 column 1
Row 2 column 2
x2+5x+6=0x^2 + 5x + 6 = 0
Row 2 column 4
Row 2 column 5
Row 3 column 1
Row 3 column 2
a2+b2=c2a^2 + b^2 = c^2
Row 3 column 4
Row 3 column 5

Learning

2 boxes
3 steps

How to work with tree diagrams

This idea appears again in the higher-mark questions, so it is worth over-learning.
  1. Read the question and write down what is being asked for.
  2. Set out the working for tree diagrams 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: a2+b2=c2a^2 + b^2 = c^2
2 rules

Key facts: Tree diagrams

The examiner marks the working, so a correct answer with no method still drops marks.

  • Rule 1

    How tree diagrams behaves in the 1st of the cases the specification names.
    ≈160\approx 160

  • Rule 2

    How tree diagrams behaves in the 2nd of the cases the specification names.
    49=7\sqrt{49} = 7

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Examples

2 boxes
2 marks · worked

Worked example: tree diagrams

This idea appears again in the higher-mark questions, so it is worth over-learning.
The layout below is the one the mark scheme expects.

Diagram showing tree diagrams laid out step by step

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

Practice question 6: ≈160\approx 160

Work through the method one line at a time and write down what changes at each step.

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Common questions

How many marks is tree diagrams usually worth?
Between one and four, depending on how many steps the question asks for.
Is this on the A Level Economics OCR paper?
Yes — it sits in the Markets and demand strand.