Subtraction to 20

Part of MathsAdding and subtractingYear 2

What is subtraction?

Subtraction is taking away one number from another.

When you subtract it gives you the difference between two numbers.

A subtraction is written using a minus sign (-) between two numbers, like this:

12 - 4 = 8

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Quiz: Subtraction to 20

Take this quiz to see how much you know about this topic already, then work through the guide and see if you can beat your score.

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Subtraction by counting back

Take a look at this number line. It shows 14 - 5 = 9.

You can count backwards down the number line to subtract.

Number line from 0 to 20. There are jumps of 1, so 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20. An arrow points back from highlighted 14 to highlighted 9. The number 5 is above the arrow.

There are different ways you can say this calculation. You could say:

"14 take away 5 is 9."

"14 subtract 5 equals 9."

"14 minus 5 equals 9."

"The difference between 14 and 9 is 5."

However, they all mean the same thing.

Now look a this number line.

Number line from 0 to 20. There are jumps of 1, so 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20. 2 arrows jump back. First arrow from 15 to 10 with - 5 above and second arrow from 10 to 6 with - 4 above.

It shows 15 take away 9. Written as a subtraction it is:

15 - 9

You can use the number line to help us solve this subtraction.

What number do you start from?

You need to start at 15. It is easy to jump back to 10 without counting.

15 – 5 = 10

Then count back another 4, so you take away 9.

Can you see that 15 take away 9 is 6?

15 – 9 = 6

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Using a part-whole model to subtract

A part-whole model can be used to help us understand subtraction.

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  1. A part whole model with two parts containing the numbers 2 and 3. The whole contains the number 5

    This is a part-whole model. It has two parts that add up to a whole.

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Counting on to find the difference

You can count on to find the difference between two numbers.

Let's find the difference between 8 and 15.

Can you use these blocks to help you work out the answer?

2 lengths of interlocking cubes top row of 8 and underneath and lined up, a row of 15. Arrow showing the difference of 7.

You could also use a number line to count on.

Number line 0 – 20 with jumps shown forward with an arrow from 8 to 10, with 2 written above, then a jump to 15 with an arrow and 5 written above.

Count on from 8 to 10, which is 2.

Then count on from 10 to 15, which is 5.

2 + 5 = 7

The difference between 8 and 15 is 7.

15 - 8 = 7

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Example

Isma and Harry with 18 and 13 butterflies recorded in their tick box pictogram recording sheet, so the rows can be compared. Isma has 18 butterflies and Harry has 13.

Isma and Harry go on a butterfly count in a wildlife area. Isma counts 18 butterflies and Harry counts 13 butterflies.

How many more butterflies did Isma count than Harry?

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More on Adding and subtracting

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