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Tree diagrams

Tree diagrams for GCSE Engineering OCR Foundation: what it means, how to set the working out, and the questions it is asked in.
  • GCSE
  • OCR
  • Engineering
  • Foundation
  • Spec N20 · N17 · N11
  • 12 min read
  • 6 revision boxes

Introduction

2 boxes
4 min read

What is tree diagrams?

Listen to this box

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.
4 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
Row 1 column 1
Row 1 column 2
49=7\sqrt{49} = 7
Row 1 column 4
Row 2 column 1
Row 2 column 2
34×25\frac{3}{4} \times \frac{2}{5}
Row 2 column 4

Learning

2 boxes
5 steps

How to work with 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.
  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.
  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: x2+5x+6=0x^2 + 5x + 6 = 0.
Answer: x2+5x+6=0x^2 + 5x + 6 = 0
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.
    49=7\sqrt{49} = 7

  • Rule 2

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

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Examples

2 boxes
2 marks · worked

Worked example: tree diagrams

Work through the method one line at a time and write down what changes at each step.
Worth knowing: 49=7\sqrt{49} = 7.
4 marks · worked

Practice question 6: a2+b2=c2a^2 + b^2 = c^2

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 tree diagrams laid out step by step

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

Practice bank

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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 GCSE Engineering OCR Foundation paper?
Yes — it sits in the Markets and demand strand.