1. 2.NBT.9 Solve Problems and Explain Why Strategies Work
2.NBT.9 Explain why addition and subtraction strategies work, using place value and the properties of operations 1.
1 Explanations may be supported by drawings or objects
Table 1 from the common core document glossary pg. 89 can be used to find the different addition and subtraction situations.

2. Karen and Jake have a collection of 26 cars. Karen has 12 cars
Karen and Jake have a collection of 26 cars. Karen has 12 cars. How many cars does Jake have?
Be prepared to explain your answer.
Change unknown/ Put together
We want students to solve this in a variety of ways. Not only is the answer important but the way in which they solved it. One way to start is to give partners or small groups a way to solve and then they can present their strategy and solution. Possible ways to solve the problem: using addition, using subtraction, draw a picture or tape diagram, use the knowledge of doubles (Karen has 12, so Jake must have 12 plus 2 more to make 26).

3. I have 2 dozen cookies. My grandma made 10 homemade cookies
I have 2 dozen cookies. My grandma made 10 homemade cookies. The rest were store bought. How many cookies were store bought?
Be prepared to explain your answer.
Change unknown/ Put together
Students may choose the way in which they want to solve.

4. I have some pencils. My friend gave me 12 pencils
I have some pencils. My friend gave me 12 pencils. I have a total of 42 pencils. How many pencils do I have altogether?
Be prepared to explain your answer.
Start Unknown/ Add To
This is a different problem structure. You can follow the same model of first giving a way to solve the problem to small groups and have them present their solutions and then allow students to choose their own strategy.
Possible ways to solve the problem: using addition, using subtraction, draw a picture or tape diagram.

5. Some bunnies sat on a hill. 13 more bunnies hopped up the hill
Some bunnies sat on a hill. 13 more bunnies hopped up the hill. There are a total of 27 bunnies on the hill. How many bunnies were on the hill before?
Be prepared to explain your answer.
Start Unknown/ Add To

6. 16 marbles were on the table. Some rolled off. Then there was 7 marbles. How many marbles rolled off?
Be prepared to explain your answer.
Change Unknown/ Take From

7. 37 cups of Lemonade were for sale at the fair
37 cups of Lemonade were for sale at the fair. some cups of lemonade were sold. I hade a total of 14 cups of lemonade left. How many cups of lemonade were sold?
Be prepared to explain your answer.
Change Unknown/ Take From

8. Pablo has 9 trophies. He has two trophy cases
Pablo has 9 trophies. He has two trophy cases. What are the different ways Pablo can display his trophies in the trophy cases?
Be prepared to share
Both Addends unknown
Students can show all the ways to make 9.
9 + 0 = 9
8 + 1 = 9
7 + 2 = 9…

9. Add 27 + 25 What are some different ways to solve this problem?
Here we are looking for
place value strategies, for example, = 40 and = 12 so = 52.
Decomposing 27 into 25 and 2. So, = 50 plus 2 more, the answer is 52

10. Solve 3 + 4 + 9 = Student's can use: associative property
(3 + 4) + 9 = 7 + 9
The answer is 16
Decomposing (decompose 4 into 3 and 1) =

11. Subtraction
87 – 59 =
Students could use place value strategeis, decomposing and composing and an open numberline.

12. Critique the reasoning of others Is Jamie correct? Subtract 56 - 34
I know that I need to add 2 to the number 4 to get to 6. I also know that I need to add 20 to 30 to get to 50. So the answer is 22.