Subtracting negative numbers

Home learning focus

In this lesson you will learn how to subtract negative numbers.

This lesson includes:

  • a learning summary
  • two activities

Learn

Recap: Subtracting positive numbers

You can use a number line to help you subtract positive numbers.

Start from 0 and find the starting number in the calculation, and locate it on the number line.

When subtracting positive numbers, count to the left from this starting number by the next number in the calculation.

Example

Let's look at an example.

Calculate 4 – 5 – 3

Starting from zero, count up to 4.

Then subtract 5.

Then subtract 3.

So, 4 – 5 – 3 = –4

The answer is –4.

Calculations with two signs next to each other

Sometimes a calculation will have two signs, either + or , next to each other.

For example:

  • 6 + –3
  • 4 – –3
  • 6 – +3

If the signs are different, you always subtract.

If the signs are the same, you always add the numbers together.

  • 6 + –3 = 6 – 3 = 3
  • 4 – –3 = 4 + 3 = 7
  • 6 – +3 = 6 – 3 = 3

Subtracting negative numbers

In a calculation, if the signs are the same you always add the numbers together. So two negatives always equal a positive.

Therefore, 4 – –3 is the same as 4 + 3, which equals 7.

More examples

  • 5 - -15 = 5 + 15 = 20

  • -5 - -15 = -5 + 15 = 10

Practise

Activity 1

Negative numbers in context

Have a go at this worksheet from Whizz Education. You can print it out or write your answers on a piece of paper.

You will answer equations using negative numbers and two signs.

Subtracting negative numbers

Activity 2

Negative number pyramids - subtraction

Have a go at this worksheet from Teachit. You can print it out or write your answers on a piece of paper.

You have to complete the missing numbers in each pyramid. Subtract the two adjacent cells left to right to get the value of the cell above.

Negative number pyramids - Subtraction

There's more to learn

Have a look at these other resources around the BBC and the web.

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KS3 Maths
BBC Bitesize Daily
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11 - 14 Maths
Quiz: Do you know your prequels?
Simon Singh's Numbers