1. Choosing a Strategy
Unit of Study 5: Modeling and Representing 2-Digit Addition and Subtraction
Global Concept Guide: 3 of 3

2. Content Development
Over these five days, students will spend time working in groups, pairs or independently to select and use a variety of strategies they have been taught over the last two weeks.
At this point, very few students should still need to use base ten blocks. Most students should be able to use quick pictures, open number lines, make a ten, and record and explain their thinking in their notebooks.
These strategies will be important as students apply them in adding and subtracting 3 digit numbers.

3. Day 1
Essential question: How can I apply efficient strategies to real-world situations in a 2-digit addition or subtraction problems?
Students should be referring back to the anchor chart as mentioned in the GCG 1 of this unit. Students should be encouraged to solve problems multiple ways to look for the strategy best for the given numbers.
Engage students with a problem such as:
Mr. Lumberjack chopped down 27 pine trees and 36 fir trees. How many trees did he chop down?
Students should discuss strategy choices and explain their reasoning.
MAFS.2.NBT.2.9 Explain why addition and subtraction strategies work, using place value and the properties of operations.
Additional problems to apply using efficient strategies.
At the end of Day 1, students will be able to select the most efficient strategy for solving word problems.

4. Day 2
Essential question: How can I determine if my answer is reasonable in a multistep problem?
It is important for students to think about what a reasonable answer will be prior to solving the problem. This is an important real life skill that students will utilize so ample time is devoted to estimation throughout this Unit and GCG. This is not a time to teach estimation, but to focus on what a reasonable answer might be.
Teachers should facilitate a discussion as to how students determined their estimate when solving the problem.
When given a problem like : “ Ms. Hines had 24 chocolate chip cookies, 18 peanut butter cookies, and 26 sugar cookies. How many cookies does she have?”
When students estimate they might say things like:
“I’m putting all the cookies together so my number should increase.”
“All my numbers are close to 20 and I want to put them all together so my answer should be around 60.”
Have students then actually solve the problem to see if their answer was reasonable.
Additional problems to use to have students to determine a reasonable answer.
By the end of day 2, students will be able to determine if their answer is reasonable in a multistep problem.

5. Day 3 and Day 4
Essential question Day 3: How can I solve multistep word problems using efficient strategies?
Essential question Day 4:: How can I explain my thinking in solving a multi-step word problem?
The focus of these two days is for students to solve multistep problems using efficient strategies and explaining their thinking. KWPL, bar model, problem solving strategies, and determining reasonable answers are important skills for students to master. Make sure students have opportunities to solve problems in multiple ways and explain their thinking.
Problems to use for students to solve.
By the end of Day 3, students will be able to solve multistep problems using efficient strategies.
By the end of Day 4, students will be able to explain their thinking about their solution strategy to a multistep problem.

6. Day 5
Essential question: How can I apply efficient strategies in problem solving?
This day will give you time to differentiate with your students.
For students that need additional support you may need to go back to fact strategies- make a ten, open number line, base ten blocks, quick pics, and number bonds. Students also may need support in problem solving strategies using a graphic organizer like KWPL and thinking about what a reasonable answer might be. Use problems similar to those used throughout the unit.
Enrich pages want to use with need an extension.
E42, E43, E44 E52, E53, E54
By the end of Day 5 students should be able to apply efficient strategies to problem solving.