Break Apart to Subtract Within 20
Split a teen number into 10 and ones, subtract from the 10, then put the ones back.
A teen number is a ten plus some ones. 13 is 10 and 3. When the number you subtract is bigger than those ones, do not try to subtract from the ones. Take it from the 10, then put the ones back on. Subtracting from 10 is a fact you already know.
13 − 5. The 3 cannot cover 5, so split 13 into 10 and 3. 10 − 5 = 5. The 3 was not used, so add it back: 5 + 3 = 8. 13 − 5 = 8.
10 − 5 = 5
Subtract from 10.
5 + 3 = 8
Add the ones that were left.
- Split the teen number into 10 and ones.
- Subtract from the 10.
- Add the ones back on.
- The ones are not subtracted. They come back at the end.
12 − 4: 12 is 10 and 2. 10 − 4 = 6, then 6 + 2 = 8. 15 − 7: 15 is 10 and 5. 10 − 7 = 3, then 3 + 5 = 8. 14 − 6: 10 − 6 = 4, then 4 + 4 = 8.
Watch out
- Trying to subtract from the ones and stopping when it will not go.
- Forgetting to add the ones after the 10 is used.
- Subtracting from both the 10 and the ones.
What is 12 − 4?
12 is 10 and 2. 10 − 4 = 6, then 6 + 2 = 8.
What is 15 − 7?
15 is 10 and 5. 10 − 7 = 3, then 3 + 5 = 8.
Math practice for Break Apart to Subtract
Subtract within 20
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