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Strategies to Add & Subtract within 20 (Make a 10 & Doubles Facts)
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What you will learn from this videoWhat you will learn
- How to use doubles facts to add & subtract numbers up to 20.
- How making a ten can help us add & subtract numbers up to 20.
- How this knowledge can help us race toy cars, go to a costume party, and even make banana splits!
- Discussion Questions
Before Video
What does it mean to decompose a number?ANSWERYou break that number into two parts. The sum of the two parts is the original number.
Answers will vary. Sum of two given numbers should add to 10.
The one in the number tells me that there is a 10. The second digit tells me how many more. 18 is 10 and 8 more.
You can move 3 counters over to the 7. 7 + 3 = 10. Then there are 5 counters left. So, it is 10 and 5 more.
The counters originally showed 7 + 8. Now they show 10 + 5 = 15.
After Video
What strategy would you use to find 6 + 7? ANSWERAnswers will vary. Students may make a 10 by adding 6 + 4 + 3. Students may use a doubles fact: 6 + 6 + 1.
Answers will vary. Students may make a 10 by adding 8 + 2 + 2. Students may use doubles facts and add 4 + 4 + 4.
Answers will vary. Students may say they always use one strategy or that they choose the doubles strategy if the addends are the same or 1 apart.
Answers will vary. Students may describe a counting back strategy: 14 – 4 = 10, 10 – 3 = 7. They may count on 7 + 3 = 10, 10 + 4 = 14. 3 + 4 = 7. Students may also remember that 14 and 7 are part of a doubles fact, so the difference must be 7.
Answers will vary. Students may say they always use one strategy or that they choose the count on strategy when they have to 'cross 10' when subtracting.
- Vocabulary
- Addition DEFINE
Finding the total, or sum, by combining two or more numbers.
- Sum DEFINE
The result of adding.
- Subtraction DEFINE
Taking one number away from another.
- Difference DEFINE
The result of subtracting.
- Decompose DEFINE
Breaking a number into two or more parts.
- Make Ten Strategy for addition DEFINE
When adding two numbers, break one number into two parts, so that one part added to the first number makes 10.
- Doubles Strategy for addition DEFINE
When adding two numbers, break one number into two parts so that two of the numbers make a doubles fact.
- Count On Strategy for Subtraction DEFINE
When subtracting two numbers, count on from the smaller number to the bigger number. How many you counted on is the difference.
- Count Back Strategy for Subtraction DEFINE
When subtracting two numbers, count back from the bigger number the amount given by the smaller number. Where you stop counting is the difference.
- Addition DEFINE
- Reading Material
- Practice Word Problems
- Practice Number Problems
- Lesson Plan
- Teacher Guide
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