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

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 VideoWhat 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.

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
Download as PDF Download PDF View as Separate PageWHAT IS A STRATEGY?A strategy is a way you can tackle a problem. In math, there are often many strategies you use to solve a problem. These strategies can all give you the correct answer! Just pick the one that makes the most sense to you.
To better understand strategies…
WHAT IS A STRATEGY?. A strategy is a way you can tackle a problem. In math, there are often many strategies you use to solve a problem. These strategies can all give you the correct answer! Just pick the one that makes the most sense to you. To better understand strategies…LET’S BREAK IT DOWN!
Counting all to find a sum.
You have 9 toy cars and 7 toy cars. How many cars do you have in all? 9 + 7 = ? You can count all of the cars to find the sum. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16. There are 16 cars in all.
Counting all to find a sum. You have 9 toy cars and 7 toy cars. How many cars do you have in all? 9 + 7 = ? You can count all of the cars to find the sum. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16. There are 16 cars in all.Make a ten to find how many cars.
Counting all of the cars will get you the correct answer but it takes a long time. Especially when numbers get bigger! You can make a ten to find how many in all. 9 + 1 = 10, so take 1 from 7 and add it to the 9. That leaves 6 left. So, 9 + 7 = 10 + 6. There are 16 cars in all.
Make a ten to find how many cars. Counting all of the cars will get you the correct answer but it takes a long time. Especially when numbers get bigger! You can make a ten to find how many in all. 9 + 1 = 10, so take 1 from 7 and add it to the 9. That leaves 6 left. So, 9 + 7 = 10 + 6. There are 16 cars in all.Use doubles facts to add spots.
A Dalmatian has 8 spots and 9 spots. How many spots in all? 8 and 9 are close to a double. 8 + 8 = 16. 9 is 1 more than 8. So 8 + 9 is the same as 8 + 8 + 1, or 16 + 1 = 17. There are 17 spots in all.
Use doubles facts to add spots. A Dalmatian has 8 spots and 9 spots. How many spots in all? 8 and 9 are close to a double. 8 + 8 = 16. 9 is 1 more than 8. So 8 + 9 is the same as 8 + 8 + 1, or 16 + 1 = 17. There are 17 spots in all.Count to compare cherries.
A jar has 15 cherries. You use 9 cherries. How many cherries are left? You can count back from 15 to 9 find the difference. 14, 13, 12, 11, 10, 9. You can also count on to find a difference. Count on from 9 to 15. 10, 11, 12, 13, 14, 15. You counted 6 numbers both ways. There are 6 cherries left.
Count to compare cherries. A jar has 15 cherries. You use 9 cherries. How many cherries are left? You can count back from 15 to 9 find the difference. 14, 13, 12, 11, 10, 9. You can also count on to find a difference. Count on from 9 to 15. 10, 11, 12, 13, 14, 15. You counted 6 numbers both ways. There are 6 cherries left.Make a ten to subtract.
You can make a ten to subtract. Start with 15 cherries. 15 is 10 and 5 more, so break 9 into 5 and 4. Subtract 5: 15 – 5 = 10. Then subtract 4 more. 10 – 4 = 6. So, 15 – 9 = 6.
Make a ten to subtract. You can make a ten to subtract. Start with 15 cherries. 15 is 10 and 5 more, so break 9 into 5 and 4. Subtract 5: 15 – 5 = 10. Then subtract 4 more. 10 – 4 = 6. So, 15 – 9 = 6. 
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Science & Math$_{/yr}

Science Only$_{/yr}
There are 9 apples and 6 pears in a bowl. Use counting to find the total number of pieces of fruit that are in the bowl.
Tasha has 9 flowers. Dane has 5 flowers. Use the Make Ten strategy to find how many flowers they have all together.
There are 14 strawberries in a basket. Cheryl puts 6 strawberries in her bowl. How many strawberries are left in the basket?
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