How to add and subtract positive and negative numbers

Part ofMathsPositive and negative numbers

Key points

  • There are rules for adding and subtracting and 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 .

  • 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

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  1. 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.

Example: calculate (-6) + 8

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  1. Number line showing minus ten to ten with example minus six plus eight.

    Work out (-6) + 8

Example: calculate (-4) - 3

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  1. Number line showing minus ten to ten with example minus four minus three.

    Work out (-4) – 3

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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.

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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
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
Negative numbers are used when freezing temperatures fall below zero.
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More on Positive and negative numbers

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