1. Adding and Subtracting 10
Unit of Study 9: Two Digit Addition and Subtraction
Global Concept Guide: 1 of 3

2. Content Development
“As children begin adding tens, some may still need to use cubes or base-ten blocks to show the tens before drawing quick pictures.” – Go Math Chapter 8 About the Math p. 321B
If a student is able to mentally add or subtract tens, this will help the student decompose larger numbers to add and subtract.

3. Problem Solving Scenarios- Different Types
Problem Types
Throughout this unit, use a variety of problem types for addition and subtraction. Students had explicit instruction with these problem types in Unit 1.
Below is a link with problem scenarios for each type. The teacher can print the scenarios and add two digit numbers to match the first grade standards. (scroll down to the bottom of the webpage  )
Problem Solving Scenarios- Different Types

4. Open Number Lines
Open number lines help students internalize the patterns they have observed when adding and subtracting with ten. The purpose of the open number line is to allow students to choose their own intervals; therefore there will be more than one acceptable representation. This is a great opportunity for student discussion.
The open number line can be used as a strategy for adding and subtracting tens.
The use of the open number line to add and subtract tens will lay the foundation for adding & subtracting two digit numbers, such as

5. Day 1 Essential Question: How can you show adding tens?
On Day 1, students will be adding tens to a decade number (10, 20, 30, 40, 50, 60, 70, 80, 90). Students will use a hundreds chart, base ten models, and open number lines to solve these problems.
For Example: Mrs. James sharpens 10 pencils. If Mrs. James sharpens another 20 pencils. How many sharpened pencils does Mrs. James have?
This hundred chart shows students starting at 10 pencils and counting by tens to a total of 30. Students could use clear counters to place on the hundred charts or use dry erase markers to track their thinking. (Click 4 times to see 100 chart example.)
To increase fluency with adding tens, teachers may want to spend a few minutes in the beginning of a lesson using a class hundred chart. Teachers could select number, have students add 10 or subtract 10, and provide reasoning.

6. Day 1 Continued… Essential Question: How can you show adding tens?
Engage: Use the word problem with sharpened pencils on the previous slide. Students can use base ten blocks, a hundreds chart, or draw quick pics of the base ten blocks.
Building Conceptual Knowledge: Go Math Lesson 8.2, Listen and Draw p. 321 Students will add 30 pennies to a group of 20 pennies. Students should explain their thinking.
Share student strategies: connect hundreds chart with base ten blocks/quick pics. How the models are similar? What change happened in the tens place value? Why? What change happened in the ones place? Why?
Pose the problem about Kyle’s pennies from Go Math p. 321 (TE manual) Follow the same routine as the previous problem.
Pose problems to students that are not the result unknown problem structure. For example- Ashli has 20 pennies. Kelly gave her some pennies. Now, Ashli has 60 pennies. How many pennies did Ashli receive from Kelly? See the Problem Type on slide 2 for a link with more scenarios.

7. Day 1 Continued… Essential Question: How can you show adding tens?
Have students model adding tens to a decade number by completing Go Math On Your Own p. 323 #s Students should be using base ten blocks, a hundreds chart, or drawing quick pics. Problem #9 will provide the sum of 50 and students have to find both addends.
Closure: Explain how you can add tens using a hundreds chart.
By the end of Day 1, students should be able to add tens to a decade number using base ten blocks or hundreds chart.

8. Day 2
Essential Question: How can you show adding tens to any two digit number?
Engage: Pose the problem solving scenario to students. Alice has 22 flowers. Then she picks 30 more flowers. How many flowers does Alice pick? Students can select base ten blocks or hundreds chart to track their thinking. Share student strategies and how they connect to each other. Emphasize what is happening in the tens and ones place value.
Building Conceptual Knowledge: Go Math Lesson 8.4, Problem Solving p. 332 #s 14, 16 and Problem Solving p. 336 #s 18, 19. These problems can be posed to students and build understanding of adding tens to any two digit number.

9. Day 2 Continued…
Essential Question: How can you show adding tens to any two digit number?
Independent Practice: Use the resource, Adding Tens to a Two Digit Number Task. In this task, students will select a two digit number and a decade number from two different piles. The task shows adding with base ten blocks but a hundreds chart would also be applicable.
Go Math Share and Show p. 330 #s 2,4 and On Your Own p #s 5,8,10,11 could also be used for independent practice. These problems are the only ones that match the essential question for this day. The other problems will be used on Day 2 in GCG 2.
By the end of Day 2, students should be able to add tens to a given number using base ten blocks or a hundreds chart. Students should be able to communicate the changes in the tens and ones place value.

10. Day 3 Essential Question: How can you show subtracting tens?
Engage: Go Math Lesson 8.3, Listen and Draw p In this task, students explore the concept of subtracting tens from a decade number. Use the guiding questions on p. 325 (TE Manual). Use the second problem solving scenario on Go Math p. 325 (TE Manual).
Remember to share student strategies and the connection with one another.
Building Conceptual Knowledge: Pose problem solving scenarios to your students and have students use models, number lines, and 120 chart to solve subtracting groups of ten from a decade number. For example: Ashley’s mom bought 7 boxes of Capri Suns with ten in each box. At Ashley’s party her friends drank 30 drinks. How do you know how many drinks Ashley has left?
Independent Practice: Go Math On Your Own p. 327 #s Students will draw a base ten model to show the subtraction of tens.
Closure: Go Math On Your Own p. 327 #9. This problem has a change unknown. Students can complete this problem in a math journal.
By the end of Day 3, students should be able to subtract tens from a decade number. Students should be able to draw a base ten model or use the hundreds chart.

11. Day 4
Essential Question: How can you mentally solve 10 more or 10 less than any two digit number?
Engage/Building Conceptual Knowledge: Mentally 10 More or Less
This lesson focuses on mentally 10 more or 10 less. The students are guided through using a hundred chart to reinforce 10 more/10 less. There are teacher questions for scenarios to pose to the students.
Use the +10/-10 worksheet for independent practice.
10 more or 10 less game: This game roll a die and need to find 10 more or 10 less on their game board. Numeral cards 0-20 could be used instead of the 20 sided dice.
Independent Practice: 10 More or Less Students have to record the number that is ten more or ten less than the given two digit number. Students may use the hundreds chart for this task, however, you want students to recognize place value patterns and start mentally computating 10 more or 10 less.
As students are working on the 10 more or 10 less independent practice, teacher should probe individual students to determine if they can mentally add 10 more or 10 less. The teacher will select a different number for each student and check off if the student is able to mentally solve 10 more or 10 less (without hundreds chart or other tools). Use your professional judgment about whether students are mentally solving in sufficient amount of time. 10 More or Less Recording Sheet
By the end of Day 4, students should be able to mentally add ten more or subtract ten from a two digit number.

12. Enrich/Reteach/Intervention
Add Decade Numbers: This resource is adapted from Engage New York Module. It is five pages long- it is suggested for the teacher to purposefully select which problems fit their students. It could be used for reteach or core depending on which problems are selected.
Reteach:
Adding sets of 10- This task utilizes base ten blocks to see patterns when adding tens.
Add/Subtract Tens: Depending on the support needed, students can use the base ten models to add a decade number to a two digit number or build their own models for the problems listed at the bottom of the resource.
Add Tens: Students will add tens from a given number. Base ten blocks and hundreds chart could be utilized to support the counting of tens.
10 More/10 Less: This resource has opportunities to add 10 more or 10 less than a number.
Core/Enrich:
Adding/Subtracting Tens Word Problems: Students will solve different word problem structure types using adding and subtracting tens. The resource was created from the rainforest problem types structure from the website on slide 3.

13. Literature for your Classroom Library