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# Week 4 - 8 Addition and subtraction

National curriculum content

• Add and subtract numbers mentally, including:
• A three-digit number and ones
• A three-digit number and tens
• A three-digit number and hundreds
• Add and subtract numbers with up to three digits, using formal written methods of columnar addition and subtraction
• Estimate the answer to a calculation and use inverse operations to check answers
• Solve problems, including missing number problems, using number facts, place value, and more complex addition and subtraction

Lesson objectives

1. Add and subtract multiples of 100
3. Add and subtract 3-digit and 1-digit numbers - not crossing 10
4. Add a 2-digit and 1-digit number - crossing 10
5. Add 3-digit and 1-digit numbers - crossing 10
6. Subtract a 1-digit number from 2-digits - crossing 10
7. Subtract a 1-digit number from a 3-digit number - crossing 10
8. Add and subtract 3-digit and 2-digit numbers - not crossing 100
9. Add 3-digit and 2-digit numbers - crossing 100
10. Subtract a 2-digit number from a 3-digit number - crossing 100
12. Spot the pattern
13. Add two-digit numbers - crossing 10
14. Subtract a 2-digit number from a 2-digit number - crossing 10
15. Mixed addition and subtraction problems
16. Add and subtract 2-digit and 3-digit numbers - not crossing 10 or 100
17. Add 2-digit and 3-digit numbers – crossing 10 or 100
18. Subtract a 2-digit number from a 3-digit numbers – crossing 10 or 100
19. Add two 3-digit numbers – not crossing 10 or 100
20. Add two 3-diit numbers – crossing 10 or 100
21. Subtract a 3-digit number from a 3-digit number – no exchange
22. Subtract a 3-digit number from a 3-digit number – exchange

What we want children to know

• Recognise patterns when we add and subtract 1, 10 and 100
• Know and understand place value and that ten ones are the same as one ten
• Learn that we can only hold single digits in each column, anything over must be exchanged
• Partition two-digit numbers in order to add and subtract from them
• Show addition and subtraction using different representations such as Base 10, arrows cards and place value charts
• Use their knowledge of inverse to work out missing number problems
• Use the column method, when appropriate, to solve addition and subtraction calculations
• Develop flexibility and be able to select the most effective method
• Check how reasonable their answers are and refer to ‘near numbers’
• Explore ways of checking to see if an answer is reasonable

What skills we want children to develop

Use knowledge to solve Reasoning and Problem Solving questions such as:

True or False?

Are these number sentences true or false?

E.g. 597 _ 7 = 614               804 – 70 = 744                    768 + 140 = 909

Convince Me:

_ _ + _ _ + _ _

The total is 201. Each missing digit is either a 9 or a 1. Write in the missing digits.

Is there only one way of doing this or lots of ways? Convince me.

Always, Sometimes, Never:

Is it always, sometimes, never true that if you subtract a multiple of 10 from any number the ones digit of that number stays the same.

Mathematical talk

• How many different ways can you represent 200 + 300?
• Using Base 10, can you partition your numbers?
• How many tens can we add to 352 without exchanging?
• How many ones do we need to exchange for one ten?
• What do you notice when we add and subtract 100s from a 3-digit number?
• Do we need to write a zero in the hundreds column when there are no hundreds left?
• Can you draw a picture of this representation?
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