Starter quiz
- 40 can be partitioned into 30 and ______
- 10 ✓
- 20
- 30
-
- How can 60 be partitioned into two parts?
- 30 and 30 ✓
- 20 and 30
- 20 and 40 ✓
- 10 and 50 ✓
-
- 95 + ______ = 100
- '5' ✓
- 150 + ______ = 200
- '50' ✓
- 300 − 6 = ______
- '294' ✓
The total height of Peter and the boxes is 300 cm. Peter is 80 cm tall. How high are the boxes?- 120 cm
- 220 cm ✓
- 280 cm
- 292 cm
-
Exit quiz
- How would you partition 6 to calculate 97 + 6 efficiently?
- add 3 then add 3 ✓
- add 2 then add 4
- add 1 then add 5
-
- How would you partition 7 to calculate 105 − 7?
- subtract 2 then subtract 5
- subtract 3 then subtract 4
- subtract 4 then subtract 3
- subtract 5 then subtract 2 ✓
-
- Which calculations cross a 100s boundary?
- 90 + 20 ✓
- 120 + 30
- 190 − 20
- 220 − 30 ✓
-
- 220 − 30 = ______
- '190' ✓
Use the number line to complete the calculation. 370 + ______ = 420- '50' ✓
Use the number line to complete the calculation. 550 − ______ = 480- '70' ✓
Worksheet
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Presentation
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Lesson Details
Key learning points
- Addition and subtraction calculations can represent counting on and back over the 100s boundary.
- When you count on in tens, sometimes the 10s digit only changes and sometimes the 100s digit changes.
- When you count back in tens, sometimes the 10s digit only changes and sometimes the 100s digit changes.
Common misconception
Pupils may partition numbers incorrectly when adding or subtracting across a 100s boundary.
Encourage pupils to add or subtract to first the 100s number, using number pairs that total 10 or 100.
Keywords
Bridging - A mental strategy which uses addition or subtraction to cross a number boundary.
Partition - Splitting an object or value down into smaller parts.
100s boundary - The point at which numbers change into 100s numbers, or from one set of hundreds to another.
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