**Addition and Subtraction to 20**

Students use addition and subtraction facts to 10 to calculate answers to addition and subtraction questions to 20. There are various strategies that can be used. When adding numbers it is generally a good idea to start with the largest number, so you have less to add.

8 + 6 = ?

So 8 + 6 = 14.

16 - 9 = ?

So 16 - 9 = 7.

4 + 7 + 6 + 5 + 3 = ?

Look for the best friends that add to 10: 4 + 6 = 10 and 7 + 3 = 10

10 + 10 + 5 = 25

So 4 + 7 + 6 + 5 + 3 = 25

18 - 3 - 7 = ?

Look for numbers that add to 10: 3 + 7 = 10

18 - 10 = 8

So 18 - 3 - 7 = 8

20 - 4 - 3 - 6 = ?

Look for numbers that add to 10: 4 + 6 = 10

20 - 10 = 10 and take away 3 more: 10 - 3 = 7

So 20 - 4 - 3 - 6 = 7

**Bridging to 10****Addition**8 + 6 = ?

*Step 1*: What do we need to add to 8 to get to 10? The answer is 2, so we start by adding 2 of the 6 to 8 to get 10.*Step 2*: How many more do we need to add? 6 - 2 = 4. We need to add 4 more: 10 + 4 = 14.So 8 + 6 = 14.

**Subtraction**16 - 9 = ?

*Step 1*: Take 6 from 16 to get to 10.*Step 2*: Work out how many more to take away: 9 - 6 = 3. We need to take 3 more away: 10 - 3 = 7.So 16 - 9 = 7.

**Grouping Numbers that Add to 10****Addition**4 + 7 + 6 + 5 + 3 = ?

Look for the best friends that add to 10: 4 + 6 = 10 and 7 + 3 = 10

10 + 10 + 5 = 25

So 4 + 7 + 6 + 5 + 3 = 25

**Subtraction**18 - 3 - 7 = ?

Look for numbers that add to 10: 3 + 7 = 10

18 - 10 = 8

So 18 - 3 - 7 = 8

20 - 4 - 3 - 6 = ?

Look for numbers that add to 10: 4 + 6 = 10

20 - 10 = 10 and take away 3 more: 10 - 3 = 7

So 20 - 4 - 3 - 6 = 7

**Using Addition Doubles**Students memorise addition and subtraction doubles to 20 as this helps later when learning the 2x table. These facts can be used to answer addition and subtraction questions.

*Number Neighbours*The addition doubles can be used to work out the answers to

*number neighbours*questions.

As 1 + 1 = 2 then 1 + 2 = 3 because 2 is 1 more than 1, so the answer is 1 more.

As 3 + 3 = 6 then 3 + 4 = 7 because 4 is one more than 3, so the answer is 1 more.

*Other Questions*As 3 + 3 = 6 then 3 + 5 = 8 because 5 is 2 more than 3, so the answer is 2 more than 6.

As 6 + 6 = 12 then 6 + 8 = 14 because 8 is 2 more than 6, so the answer is 2 more than 12.

As 14 + 6 = 20 then 20 - 14 = 6 and 20 - 6 = 14.

The inverse strategy turns subtraction into addition.

16 - 7 = ?

How much have we added altogether?

16 - 7 = 9

**Using Related Addition and Subtraction Number Facts**As 14 + 6 = 20 then 20 - 14 = 6 and 20 - 6 = 14.

**Inverse Strategy**The inverse strategy turns subtraction into addition.

16 - 7 = ?

*Step 1*: Start at 7 and add**to make 10.****3***Step 2*: Add**to make 16.****6**How much have we added altogether?

**+****3****= 9****6**16 - 7 = 9