Subtraction+Methods

__**SUBTRACTION**__ Subtraction is one of the hardest calculations that is taught to children at primary age. With the new changes in the approaches and ways maths is taught in school over the last few years, there are lots of ways to go about making the calculation more manageable and relevant for children at different ages/abilities.

__**Subtraction using a number line**__

This method of subtraction uses the child’s knowledge of finding the difference between two numbers and simple addition. There isn’t one correct way of using a number line to find the answer to a subtraction question, it is something that can be tailored by children to suit their individual needs. Eg 90-47=? So a child writes out the number being used on a number line. Then they count on from the smaller number to the bigger using ‘easy’ numbers along the way (multiples of 10 etc). Adding these numbers together then finds the answer to the initial subtraction question, the child can then re-trace steps along the number line to check the answer. 3+10+10+10+10=43 so... 90-47=43

If a child is more confident with number then a smaller amount of steps can be taken to work along the number line. Eg 90-47=? In this case, as soon as the child can make the smaller number up to a multiple of 10, they can then count on quicker in further multiples of 10 to the answer. 3+40=43 so... 90-47=43

Useful websites/resources:

[] (good downloadable resources, but you need to register a free account on the website). [] (good interactive game involving sutraction on a number line). [] (interactive resource with lots of different questions and explanations with the number line).

__**Subtraction using the extended approach**__

When children are secure with the mental calculation methods for subtraction, they move on to the expanded approach. For example, children would work out a calculation such as 87-53, in the following way: 80 7 Flash cards are usually used as a learning aid with this - 50 3 approach as they clearly show what is happening.

30 4

so 87 - 53 = 34

This is used to develop a more compact method. The word "and" is used to show what the numbers are partitioned into and is prefered to "+" so as not to confuse addition with subtraction. For example a calculation such as 563 - 248 would be calculated in the following way:

500 and 60 and 3 exchange 60 into a 50 and a 10 - 200 and 40 and 8

500 and 50 and 13 Numbers are "exchanged" to enable - 200 and 40 and 8 children to complete the process.

300 and 10 and 5

so 563 - 248 = 315

Useful links: - @http://www.hartfordprimaryschool.co.uk/Subtraction.pd

__**Subtraction using the 'Compensation' method**__

Another written method for subtraction is the **Compensation** method. Compensation is good for 'rounding up' to the nearest ten, or hundred (depending on how difficult the question is), **subtracting** that amount and then **adding** the difference between the subtracted amount and the rounded-up amount. This would be best explained using an example:

347 - 87


 * 1.** First, **round up** 87 to the nearest hundred, because this would be easier than working out 347 - 90. Therefore 347- 100:

347 - 100 = 247

100 - 87 = 13
 * 2.** Then find the difference between 100 and 87, which is 13.


 * 3.** Add 13 to 247, which is 260:

347 - 100 247 + 13 = 260

The answer is therefore **260**
 * Further Resources and Links using Subtraction:**
 * Further Resources and Links using Subtraction:**

[|BBC Teachers advice and ideas on planning subtraction lessons].

[|Subtraction Wipe Out Wall activity]- pupils have to see how fast they can subtract using a timer. There are a variety of levels.