Informal and mental strategies for adding and subtracting two 3-digit numbers
Informal and mental strategies for adding and subtracting two 3-digit numbers
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Threads
Why this why now
This unit develops mental strategies applied to numbers bridging 100 and applies them to adding and subtracting 3-digit numbers. Pupils consider how to partition numbers to enable them to bridge multiples of 10 and 100. They also use number lines to find the difference and make decisions on which is the most efficient strategy to add or subtracts pairs of 3-digit numbers. This consolidation of mental and informal strategies prepares pupils for the introduction of more formal strategies in later units.
Prior knowledge requirements
- Use number bonds and partitioning to simplify
- Add and subtract multiples of 10 and 100
- Use rounding and adjusting to estimate
- Interpret and present data using bar charts, pictograms and tables
Threads
Why this why now
This unit develops mental strategies applied to numbers bridging 100 and applies them to adding and subtracting 3-digit numbers. Pupils consider how to partition numbers to enable them to bridge multiples of 10 and 100. They also use number lines to find the difference and make decisions on which is the most efficient strategy to add or subtracts pairs of 3-digit numbers. This consolidation of mental and informal strategies prepares pupils for the introduction of more formal strategies in later units.
Prior knowledge requirements
- Use number bonds and partitioning to simplify
- Add and subtract multiples of 10 and 100
- Use rounding and adjusting to estimate
- Interpret and present data using bar charts, pictograms and tables
Informal and mental strategies for adding and subtracting two 3-digit numbers
In this unit pupils will add and subtract two 3-digit numbers using partitioning, adjusting, redistribution and bridging.
10 lessons in unit
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