Addition and subtraction strategies
Use counting on and counting back as strategies for addition and subtraction
Ce que l'enfant saura faire ensuite
- Add 8 + 3 by starting at 8 and counting on 3 (9, 10, 11)
- Subtract 12 − 3 by counting back 3 from 12 (11, 10, 9)
- Explain that counting on is a way to add
1 · Lis
You already know how to add and take away. Counting on and counting back work for both. Instead of starting from 1 every time, you start at one number and hop forward or backward.
Leo has 12 stickers and gives away 3. He starts at 12 and counts back three hops: 11, 10, 9. Leo has 9 stickers left.
When you add, start at the bigger number. That means fewer hops to count. Say each number out loud as you hop so you do not lose your place.
Counting on adds by hopping forward, and counting back subtracts by hopping backward, from one starting number.
À lire aussi
Add and subtract within 100: FAQ
Counting on is a way to add. For 8 + 3, start at 8. Then count 9, 10, 11. You counted 3 steps. You land on 11. Start with the bigger number to keep the count short.
3.1: Topic A- Subtraction
Counting back is a way to subtract. For 12 - 3, start at 12. Then count 11, 10, 9. You counted 3 steps back. You land on 9. Touch each number as you step back so you do not slip.
Properties of addition
Choosing a strategy matters. Counting on suits small adds. Making 10 suits numbers near 10. Splitting tens suits two digit sums. Try more than one way and pick the quick one. Explain why your pick works.
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