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Place value and rounding

Place value and rounding for A Level Chemistry OCR Foundation: what it means, how to set the working out, and the questions it is asked in.
  • A Level
  • OCR
  • Chemistry
  • Foundation
  • Spec R19
  • 9 min read
  • 8 revision boxes

Introduction

2 boxes
1 min read

What is place value and rounding?

Listen to this box

Transcript

A short spoken summary of place value and rounding and where it is used.

A spoken walk-through of place value and rounding before you read the notes.
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 place value and rounding laid out step by step

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

The place value and rounding reference table

This idea appears again in the higher-mark questions, so it is worth over-learning.
Term
Meaning
Example
Common slip
Marks
Row 1 column 1
Row 1 column 2
34×25\frac{3}{4} \times \frac{2}{5}
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
Row 3 column 1
Row 3 column 2
×10\times 10 moves every digit one column left
Row 3 column 4
Row 3 column 5
Row 4 column 1
Row 4 column 2
≈160\approx 160
Row 4 column 4
Row 4 column 5

Learning

4 boxes
3 steps

How to work with place value and rounding

Sketch the shape even when the question does not ask for one — it makes the next step obvious.
Worth knowing: 34×25\frac{3}{4} \times \frac{2}{5}.
  1. Read the question and write down what is being asked for.
  2. Set out the working for place value and rounding 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: a2+b2=c2a^2 + b^2 = c^2
3 rules

Key facts: Place value and rounding

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

  • Rule 1

    How place value and rounding behaves in the 1st of the cases the specification names.
    ≈160\approx 160

  • Rule 2

    How place value and rounding behaves in the 2nd of the cases the specification names.
    ×10\times 10 moves every digit one column left
3 steps

How to work with place value and rounding

The examiner marks the working, so a correct answer with no method still drops marks.
Worth knowing: ≈160\approx 160.
  1. Read the question and write down what is being asked for.
  2. Set out the working for place value and rounding 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: ≈160\approx 160
2 rules

Key facts: Place value and rounding

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 place value and rounding laid out step by step

The same idea drawn out, so the method is visible.
Worth knowing: ×10\times 10 moves every digit one column left.

  • Rule 1

    How place value and rounding behaves in the 1st of the cases the specification names.
    ≈160\approx 160

  • Rule 2

    How place value and rounding behaves in the 2nd of the cases the specification names.
    49=7\sqrt{49} = 7

  • Rule 3

    How place value and rounding behaves in the 3rd of the cases the specification names.
    ×10\times 10 moves every digit one column left

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Examples

2 boxes
4 marks · worked

Worked example: place value and rounding

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 place value and rounding laid out step by step

The same idea drawn out, so the method is visible.
Worth knowing: 49=7\sqrt{49} = 7.
4 marks · worked

Practice question 8: ≈160\approx 160

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

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Common questions

How many marks is place value and rounding usually worth?
Between one and four, depending on how many steps the question asks for.
Is this on the A Level Chemistry OCR Foundation paper?
Yes — it sits in the Number strand.