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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
2. Add and subtract 1s
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
11. Add and subtract 100s
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
23. Estimate answers to calculations

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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