1.2.3

Mental Addition & Subtraction

Test yourself on Mental Addition & Subtraction

Test your knowledge with free interactive questions on Seneca — used by over 10 million students.

Mental Addition and Subtraction

You need to think about our place value rules when adding and subtracting mentally.

4,372 + 6

4,372 + 6

  • You look at the 'ones' column because that is the column you are adding to.
    • I know that 2 + 6 = 8
    • So 4,372 + 6 = 4,378
Carrying over

Carrying over

  • Sometimes you need to carry over a value to the next column.
Carrying over example

Carrying over example

  • E.g. 4372 + 9
    • You look at the 'ones' column because that is the column you are adding to.
  • I know that 2 + 9 = 11
    • So I know that my 'ones' column will be 1 and I need to carry one ten to the 'tens' column.
    • So 4,372 + 9 = 4,381
A different method

A different method

  • There are loads of different ways to do mental addition.
  • I'm trying to do the same calculation as the previous example (4,372 + 9).
    • Instead of adding 9, I can add 10 because that's easier!
    • I know 4,372 + 10 = 4,382
    • But I've added 1 too many, so I need to take 1 away.
    • 4,382 − 1 = 4,381
    • So 4,372 + 9 = 4,381

Adding Double/Triple/Quadruple Digit Numbers in Your Head

You can also add more than one digit to a number. You can add more than one digit to a number by splitting the number into its place values.

Example

Example

  • I want to work out 4,372 + 25.
  • I can split 25 into its place values.
    • 25 = 20 + 5
First, add the 'tens'

First, add the 'tens'

  • I have split 25 into 20 + 5.
  • First, add 20 to 4,372
    • 4,372 + 20 = 4,392
Then, add the 'ones'

Then, add the 'ones'

  • Then, add 5 to 4,392
    • 4,392 + 5 = 4,397
  • So you know that 4,372 + 25 = 4,397
Adding larger numbers

Adding larger numbers

  • You can use the same process to add larger numbers in your head.
  • E.g. 4,372 + 214
    • Start by splitting 214 into 200 + 10 + 4.
Adding 214

Adding 214

  • Then add 200 to 4,372.
    • 4,372 + 200 = 4,572
  • Then add 10 to 4,572.
    • 4,572 + 10 = 4,582
  • Then add 4 to 4,582.
    • 4,582 + 4 = 4,586
Jump to other topics
1

Year 5 - Number

1.1

Number & Place Value

1.1.1The Value of Digits to Millions1.1.2Smallest & Biggest Numbers to Millions1.1.3Ordering Numbers to Millions1.1.4Counting in Powers of 101.1.5Counting in Negative Numbers1.1.6Rounding Numbers up to 1,000,0001.1.7Reading Roman Numerals
1.2

Addition & Subtraction

1.2.1Written Methods for Adding Large Numbers1.2.2Written Methods for Subtracting Large Numbers1.2.3Mental Addition & Subtraction1.2.4Rounding to Check Your Answer
1.3

Multiplication & Division

1.3.1Multiples1.3.2Factors1.3.3Prime Numbers1.3.4Prime Factors1.3.5Composite Numbers1.3.6Factor Trees1.3.7Multiplication by a 1 Digit Number1.3.8Long Multiplication Using Column Method1.3.9Times Tables1.3.10Division1.3.11Multiplying & Dividing by 10, 100 & 1,0001.3.12Square & Cube Numbers
1.4

Fractions & Decimals

1.4.1Compare & Order Fractions1.4.2Identifying Equivalent Fractions1.4.3Add & Subtract Fractions1.4.4Mixed Numbers & Improper Fractions1.4.5Multiplying Fractions by Whole Numbers1.4.6Converting Between Decimals & Fractions1.4.7Rounding Decimals1.4.8Ordering Decimals
2

Year 5 - Measurement

2.1

Measures

2.1.1Metric Measurements2.1.2Imperial Measurements
2.2

Perimeter & Area

2.2.1Perimeter2.2.2Area
2.3

Time

2.3.1Units of Time
3

Year 5 - Geometry

3.1

Properties of 3D Shapes

3.1.1Types of 3D Shapes3.1.2Faces, Edges & Vertices
3.2

Properties of 2D Shapes

3.2.1Polygons
3.3

Angles

3.3.1Angles in Degrees3.3.2Types of Angle3.3.3Finding Missing Angles
3.4

Position & Direction

3.4.1Reflection & Translation
4

Year 5 - Statistics

4.1

Graphs

4.1.1Line Graphs4.1.2Tables4.1.3Timetables
5

Year 6 - Number

5.1

Number & Place Value

5.1.1The Value of Digits to Ten Millions5.1.2Ordering Numbers to Millions5.1.3Rounding5.1.4Negative Numbers
5.2

Multiplication & Division

5.2.1Multiplication by a 2 Digit Number5.2.2Division5.2.3Multiples5.2.4Factors5.2.5Primes
5.3

Mental Maths

5.3.1Multiplying & Dividing by 10, 100 & 1,0005.3.2Addition & Subtraction5.3.3Adding & Subtracting 10, 100 & 1,0005.3.4Multiplication & Division
5.4

Order of Operations

5.4.1BIDMAS
5.5

Problem Solving

5.5.1Addition & Subtraction Multi-step Problems5.5.2Problem Solving with Proportion
5.6

Fractions & Decimals

5.6.1Simplifying Fractions Using Equivalents5.6.2Ordering Different Types of Fraction5.6.3Adding & Subtracting Fractions5.6.4Adding & Subtracting Mixed Numbers5.6.5Multiplying Fractions5.6.6Dividing Fractions by Whole Numbers5.6.7Converting Between Decimals & Fractions5.6.8Dividing Decimals
6

Year 6 - Ratio & Proportion

6.1

Ratio

6.1.1Using Ratios6.1.2Simplifying Ratios
6.2

Percentages

6.2.1Calculating Percentages
6.3

Scale

6.3.1Scale of 2D Shapes
7

Year 6 - Algebra

7.1

Sequences

7.1.1Describing Sequences7.1.2Finding Gaps in Sequences
7.2

Missing Number Problems

7.2.1Missing Number Problems
7.3

Equations

7.3.1Balancing Equations7.3.2Combining Two Variables
8

Year 6 - Measurement

8.1

Problem Solving

8.1.1Problem Solving with Measures
8.2

Unit Conversion

8.2.1Conversion Between Miles & Kilometres
8.3

Perimeter, Area & Volume

8.3.1Area8.3.2Volume8.3.3Nets8.3.4Faces, Edges & Vertices
8.4

Angles

8.4.1Types of Angle8.4.2Finding Missing Angles8.4.3Finding Missing Angles in Triangles8.4.4Vertically Opposite Angles
8.5

Circles

8.5.1Parts of a Circle
8.6

Coordinate Grids

8.6.1Positions on Coordinate Grids8.6.2Reflection & Translation
9

Year 6 - Statistics

9.1

Displaying Data

9.1.1Pie Charts9.1.2Line Graphs
9.2

Averages

9.2.1Mean

Practice questions on Mental Addition & Subtraction

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    Which of these calculations might you do to make calculating 6,786 + 9 easier?Multiple choice
  2. 2
    Which of these calculations might you do to make calculating 488 + 9 easier?Multiple choice
  3. 3
    How would you split 227 into its place values to make addition easier?Multiple choice
  4. 4
    How would you split 124 into its place values to make addition easier?Multiple choice
Answer all questions on Mental Addition & Subtraction

Unlock your full potential with Seneca Premium

  • Unlimited access to 10,000+ open-ended exam questions

  • Mini-mock exams based on your study history

  • Unlock 800+ premium courses & e-books

Get started with Seneca Premium

Written Methods for Subtracting Large Numbers

Rounding to Check Your Answer