Year 2

We know that addition and subtraction ‘undo’ each other.
We can write related number sentences.

Year 2 Unit 7

What we are learning:

• Understanding that subtraction is the inverse of addition (e.g. subtraction ‘undoes’ addition), and that addition is the inverse of subtraction is something that your child needs to experience. They need to have experience of ‘seeing’ this before they can understand it.
• Subtraction will ‘undo’ addition. So if you have 8 sweets and then are given 4 more, you will have 12 sweets altogether. If we take away/ subtract the 4 we will have the 8 sweets we started with.
• Addition will ‘undo’ subtraction. So if you have 14 sweets and take away/subtract/ give away 6 of the sweets you will have 8 sweets left. If you put the 6 sweets back with the 8 sweets you had left, then you will have the original amount you started with (14).
• Make sure that your child has lots of opportunities to do this with practical objects.
• Writing this in number sentences will help to build your child’s confidence in number. It will also help them to make mathematical connections.

ACTIVITY 1: WRITING RELATED NUMBER SENTENCES

Activities you can do at home:

From a starting point, e.g. 5 + 4 = 9 ask your child to write down other related number sentences, i.e. 4 + 5 = 9, 9 – 5 = 4, 9 – 4 = 5
Make these sentences with objects so that you know your child is not simply repeating a pattern.
Do this for other starting sentences. Remember to start with subtractions first at times, e.g. 10 – 2 = 8

Good questions to ask:

If I start with 7 and add 5 then take away 5 what number do I have?
How do you know the answer to this without working it out?
If we know that 9 + 5 = 14 what other number sentences can we write down?

If your child:

Can manage Activity 1 well
Consider an extension activity:
Write the number sentence 6 + 3 = 9 in the middle of a piece of paper.
Now talk about other things you know and can work out mentally if you know this fact. From this number sentence your child should be able to tell you what
5 + 3 would equal. They need to do this without working out 5 + 3 as a new calculation. They should be able to reason the following – because 5 is one less than 6 then the answer will also be one less.
– You know that 6 + 3 = 9 – can you use this fact to tell me what 5 + 3 would equal?
– You know that 6 + 3 = 9 – can you use this fact to tell me what 6 + 4 would equal?
– You know that 6 + 3 = 9 – can you use this fact to tell me what 8 + 3 would equal?
– You know that 6 + 3 = 9 – use this to tell me what 16 + 3 is? Your child needs to reason that 16 is ten more than 6 so the answer will also be 10 more.

Continue to explore the related facts for a number sentence. Start with simple number sentences. Encourage the child to explore – for example for the following number sentence 12 + 3 = 15 they might tell you and record the following:
6 + 6 + 3 = 15 / 6 + 3 + 3 + 3 = 15 etc