whole numbers addition & subtraction
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Whole Numbers Addition & Subtraction
Marshall Cavendish Institute
Peggy Foo
Learning Outcomes
State the purpose of number bonds Use addition and subtraction strategies
Number Bonds
Number bonds are different combinations of numbers that make up a given number.
Different Types of Bonds
2 + 3 = 5
67 - 56 = 11
7 X 8 = 5680 ÷ 10 = 8
7 – 1 + 5 x 2 = 16
Purposes
Number bonds lay a strong foundation for learning addition and subtraction efficiently.
Number bonds also enhance mental computations
Activities for Lower Grades
Using the magnets and 10-frame How many bonds are there to make 10?
Use concrete manipulative Generate different possible ways/ bonds Move to pictorial stage
Extension
What are the different sums that you can get with different sets of whole numbers?
What can you observe? What can you observe about the number in the middle? What can you observe about the sums?
Open-ended task (with more than 1 sum) Generate different possible ways/ bonds Problem-solving task
Addition Strategies using Number Bonds Near-10 Strategy
1
2
3
1
23
The Doubles Strategy
1
2
3
1
23
Addition Strategies using Number Bonds
Near-100 Strategy
245 + 98
Addition Strategies using Number Bonds
Near-100 Strategy
245 + 98
Rewrite 98 as (100-2)
Add 245 + 100 = 345
We add more than we should
345 – 2 = 343
Debriefing
The ability to see numbers in different combinations is developing number sense/ number concept.
How many ways to find the value of
43 + 29
Additional Strategies using Number Bonds
Using Hundred Chart
43 + 29 = 43 + 30-1 (near-ten strategy)= 73-1= 72
43 + 29 = 60 + 12 (place value concept)= 72
Subtraction Strategies using Number Bonds Addition bonds for Subtraction
16 – 9
Subtraction Strategies using Number Bonds Addition bonds for Subtraction
16 – 9
16 is made up of (10 + 6)
Use 10 – 9 = 1
Add 1 to 6 (remaining number in the bond)
1 + 6 = 7
Subtraction Strategies using Number Bonds Near-100 Subtraction Strategy
256 - 97
Subtraction Strategies using Number Bonds Near-100 Subtraction Strategy
256 - 97
Rewrite 97 as (100 – 3)
256 – 100 = 156
Subtract more than we should
156 + 3 = 159
How many ways to find the value of 67- 49
Subtraction (renaming once)
67-49 = 67-50 +1 (near 10 strategy)
= 17+1
= 18
67-49 = 18 (place value concept)
Place Value Concept
To add and subtract using formal algorithms
Use place value concept to develop conceptual understanding
Use base ten
Summary
Concrete-Pictorial-Abstract Approach Aim to develop conceptual understanding
before procedural understanding (Richard Skemp)
Summary Mental Strategies
involving number bondsFormal Algorithm
Addition Strategies:
1) Near-10 Strategy
2) The doubles Strategy
3) Near-100 Strategy
Place value concept
Subtraction Strategies:
1) Addition Bonds for subtraction
2) Near-100 Subtraction Strategy