What does it mean to decompose a number?

You break that number into two parts. The sum of the two parts is the original number.

What are some ways you can decompose 10?

Answers will vary. Sum of two given numbers should add to 10.

How can you show a teen number as 10 and some more?

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.

[Show students 7 counters of one color and 8 counters of a different color.] How can I group these counters to show 10 and some 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.

How can you write an addition equation to show how you grouped the counters?

The counters originally showed 7 + 8. Now they show 10 + 5 = 15.

What strategy would you use to find 6 + 7?

Answers will vary. Students may make a 10 by adding 6 + 4 + 3. Students may use a doubles fact: 6 + 6 + 1.

What strategy would you use to find 8 + 4?

Answers will vary. Students may make a 10 by adding 8 + 2 + 2. Students may use doubles facts and add 4 + 4 + 4.

How do you decide which addition strategy to use?

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.

What strategy would you use to find 14 – 7?

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.

How do you decide which subtraction strategy to use?

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.

Strategies to Add & Subtract within 20 (Make a 10 & Doubles Facts)

LESSON MATERIALS move

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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?ANSWER
  - You break that number into two parts. The sum of the two parts is the original number.
  What are some ways you can decompose 10?ANSWER
  - Answers will vary. Sum of two given numbers should add to 10.
  How can you show a teen number as 10 and some more?ANSWER
  - 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.
  [Show students 7 counters of one color and 8 counters of a different color.] How can I group these counters to show 10 and some more?ANSWER
  - 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.
  How can you write an addition equation to show how you grouped the counters?ANSWER
  - The counters originally showed 7 + 8. Now they show 10 + 5 = 15.
- After Video
  What strategy would you use to find 6 + 7? ANSWER
  - Answers will vary. Students may make a 10 by adding 6 + 4 + 3. Students may use a doubles fact: 6 + 6 + 1.
  What strategy would you use to find 8 + 4?ANSWER
  - Answers will vary. Students may make a 10 by adding 8 + 2 + 2. Students may use doubles facts and add 4 + 4 + 4.
  How do you decide which addition strategy to use?ANSWER
  - 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.
  What strategy would you use to find 14 – 7?ANSWER
  - 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.
  How do you decide which subtraction strategy to use?ANSWER
  - 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
- Sum DEFINE
- Subtraction DEFINE
- Difference DEFINE
- Decompose DEFINE
- Make Ten Strategy for addition DEFINE
- Doubles Strategy for addition DEFINE
- Count On Strategy for Subtraction DEFINE
- Count Back Strategy for Subtraction DEFINE
Reading Material
Practice Word Problems
Practice Number Problems
Lesson Plan
Teacher Guide
Assessment
Online Quiz Game Quiz PDF Exit Ticket