How To Add And Subtract Positive And Negative Numbers - BBC

Home » When Subtracting A Negative From A Negative » How To Add And Subtract Positive And Negative Numbers - BBC

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  1. Key points
  2. Adding and subtracting
    1. Example: 4 - 6
    2. Example: (-6) + 8
    3. Example: (-4) - 3
  3. Real-world example
    1. Question
  4. Practise positive and negative numbers
    1. Ordering activity
    2. Adding and subtracting quiz
  5. Real-world maths

Key points

  • There are rules for adding and subtracting positive and negative numbers.
  • If a number has no sign it usually means that it is a positive number. For example, 7 is really +7
  • Learning how to use a number line may help you with calculations.
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Adding and subtracting

When adding or subtracting negative numbers it can be useful to use a number line.

  • To add and subtract numbers always begin counting from zero.
  • When adding positive numbers, count to the right.
  • When subtracting positive numbers, count to the left.

Example: calculate 4 - 6

Image gallerySkip image gallery
  1. Number line from minus five to five with example four minus six.
    Image caption,

    To add and subtract numbers always begin counting from zero. When adding positive numbers, count to the right. When subtracting positive numbers, count to the left.

1 of 3

Previous imageNext imageSlide 1 of 3, Number line from minus five to five with example four minus six., To add and subtract numbers always begin counting from zero. When adding positive numbers, count to the right. When subtracting positive numbers, count to the left.End of image gallery

Example: calculate (-6) + 8

Image gallerySkip image gallery
  1. Number line showing minus ten to ten with example minus six plus eight.
    Image caption,

    Work out (-6) + 8

1 of 3

Previous imageNext imageSlide 1 of 3, Number line showing minus ten to ten with example minus six plus eight., Work out (-6) + 8End of image gallery

Example: calculate (-4) - 3

Image gallerySkip image gallery
  1. Number line showing minus ten to ten with example minus four minus three.
    Image caption,

    Work out (-4) – 3

1 of 3

Previous imageNext imageSlide 1 of 3, Number line showing minus ten to ten with example minus four minus three., Work out (-4) – 3End of image galleryBack to top

Real-world example

A thermometer is a number line that depicts temperature and often uses a vertical number line rather than horizontal.

When reading a thermometer:

  • zero represents 0°C
  • plus temperatures are above zero, eg 8°C counting upwards as the temperature gets warmer (positive numbers)
  • minus temperatures are below zero, eg -4°C counting downwards as the temperature gets colder (negative numbers)

Question

In the example below, what is the difference between the daytime and night-time temperatures?

Two thermometers, on showing night time temperature is minus four degrees and another showing daytime temperature is eight degrees.

Show answer

To find the difference between the two temperatures, count the steps between the two readings. Starting at -4°C move up 4 to reach zero. Then move up another 8 to reach 8°C. The difference in temperatures is 12°C.

Thermometer with arrows showing the difference between minus four degrees and eight degrees is twelve degrees.

Alternatively, we can use our knowledge of negative numbers to calculate the difference 8°C – (-4°C) = 8°C + 4°C = 12°C.

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Practise positive and negative numbers

Ordering activity

Work out the differences in temperature for each city. You might need a pencil and paper for your working out.

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Adding and subtracting quiz

Practise adding and subtracting positive and negative numbers with this quiz.

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Real-world maths

Mobile weather app showing minus three degrees
Image caption, Negative numbers are used when freezing temperatures fall below zero.

Positive and negative numbers are used in everyday life to compare values against zero.

Many people use negative numbers in their jobs, for example accountants, staff working in banks or building societies and weather presenters.

Mobile weather app showing minus three degrees
Image caption, Negative numbers are used when freezing temperatures fall below zero.
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More on Positive and negative numbers

Find out more by working through a topic

  • How to multiply and divide positive and negative numbers

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  • What are positive and negative numbers?

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