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# Copyright © Mathematics Mastery 2017
Parental Guidance
In this unit, pupils will be adding and subtracting using mental methods and using the written column method. When adding or subtracting always encourage your child to look at the calculation before working it out, to consider whether a mental or written method would be more efficient. This week focuses on using mental methods of addition and subtraction.
In Year 3, pupils have used mental strategies and written column methods of addition and subtraction with 3-digit numbers.
In Year 5, pupils will be extended to adding and subtracting 5-digit and 6-digit numbers with mental and written strategies.
Three key strategies for calculating mentally
Below are three strategies pupils will have used during this week’s learning:
Using derived facts
Partitioning
Partitioning = A way of breaking a number into at least two parts resulting in a number bond for that number, for example, 12 = 10 + 2.
Rounding and adjusting
4800—699
Unit 2: Addition and subtraction (Week 1 of 3)
If I know 3 + 4 = 7…
3 + 4 = 7
300 + 400 = 700
4 + 3 = 7
3000 + 4000 = 7000
30 + 40 = 70
70—30 = 40
700 —400 = 300
4000 + 3000 = 7000
7— 4 = 3
I know 699 is only 1 less than 700...
4100
- 700
4800
But now I’ve subtracted one too many! I need to add one back
4100
4101
+ 1
Step 1:
Step 2:
764 + 107 =
Partitioning 107 into hundreds, tens and ones:
864
+ 100
764
+ 7
871
764 — 107 =
Partitioning 107 into hundreds, tens and ones:
664
- 100
764
- 7
657