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# 1 More, 1 Less

Lesson 9 of 16

## Objective: SWBAT use a strategy to add or subtract a one within 100.

## Big Idea: My class has been learning about place value and the meaning of tens and ones. This lesson will develop knowledge of adding or subtracting one from a 2-digit number.

*30 minutes*

#### Rev Them Up

*5 min*

I will have my students play a game of "Around the World."

Directions: This is a competitive game to see who can say the correct answer first. You begin by selecting two students. These students stand up and you will ask your question. Whoever says the answer first, wins. The winner is then matched with a new person and the same process proceeds. You will continue to match the winner with a new person until everyone in the room has a turn and the final winner is produced. I love this game because it can be used in any content area. Go here to see a video of my class playing the game to compare numbers.

Examples:

*Okay, here we go, what is the answer to?*

*3+1=*

*3-1=*

*7+1=*

*7-1=*

Continue with numbers like this until everyone has a turn. This activity will be a spring board for today's lesson. My students have an in-depth knowledge of addition and subtraction with single-digit numbers. Students must develop a strong understanding of place value to use tens and ones to assist in addition and subtraction of 2-digit numbers. The Common Core standards want first graders to build the knowledge of place value to be able to complete addition and subtraction with double digit numbers. (1.NBT.C.5).

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#### Whole Group Interaction

*10 min*

I have a class number line that I will use to show my students 1 more and 1 less. This will be a great demonstration for my visual learners to see us point at our starting number and then see that 1 more is the next number we would say when counting and 1 less is counting backwards by 1.

*Students, look at the number 56 on the number line. If I wanted to add 1 more to it, how could I use the number line to find my answer? (Slide your finger over one spot; it's the next number when you count; etc.)*

*Students, look at the number 44 on the number line. If I wanted to subtract 1 from it, how could I find my answer? (Slide your finger back one number; count backwards; etc.) *

Watch the Plus 1, minus 1 on number line video and look at the picture of my student pointing out our starting number. Also, I will make sure they identify the idea that in most cases when adding 1 or subtracting 1 the tens digit stays the same. I would have students discuss briefly why the tens digit changes when we get to adding 1 when there are already 9 ones and when we get to subtracting 1 when there are 0 ones. This will be challenging for them to articulate at this point, but it will be helpful to get an idea of who is seeing the decade changes and how that relates to place value.

I will continue to give examples and ask different students to point at our starting number as we solve each problem. When I finish any demonstration or give any extensive instruction I always end it by asking my class if anyone has any questions. Often I get someone raising their hand who wants to share a comment or make an observation, but no questions. I allow this, but remind them that I am looking for questions or anyone who does not understand what we are doing.

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#### Independent Practice

*10 min*

I will have my students practice the 1 more and 1 less concept using the printable Worksheet in the resource section. Some of my students have advanced computation skills and will complete this worksheet very quickly. Yet some of my students will still rely on looking at the number line and using it to identify what is before or after. The majority of my class has mastered numbers 1-20 counting forward and backward, but some still struggle above 20. The number line will provide them a tool to refer to help solve their problems.

Watch the video in the resource section to see one student solving a problem. This activity will supply my students with practice in reasoning abstractly and quantitatively (MP2). The number line will provide my learners with a concrete method to reason out their answers and start to apply their thinking more abstractly.

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#### Closure

*5 min*

I will ask my students to turn to partner and tell them the process they will go through to find one more or less using our number line.

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- UNIT 1: Ordering Numbers
- UNIT 2: Building Counting Skills
- UNIT 3: Addition Strategies
- UNIT 4: Understanding Subtraction
- UNIT 5: Word Problems
- UNIT 6: Understanding Shapes
- UNIT 7: Fractions
- UNIT 8: Measurement
- UNIT 9: Graphs, Tables, and Charts
- UNIT 10: Place Value
- UNIT 11: Subtraction Strategies
- UNIT 12: Understanding Time
- UNIT 13: Understanding Addition

- LESSON 1: Building Numbers 11-20
- LESSON 2: Using Numbers 11-20
- LESSON 3: Place Value: Vocabulary
- LESSON 4: Groups of 10 and leftovers
- LESSON 5: How many tens?
- LESSON 6: Making Numbers
- LESSON 7: Problem Solve with an Organized List
- LESSON 8: Place Value: Vocabulary Review
- LESSON 9: 1 More, 1 Less
- LESSON 10: 10 More, 10 Less
- LESSON 11: Put Our Hands Together for Adding Tens
- LESSON 12: Knockin It Out of the Park by Subtracting Ten
- LESSON 13: Game of Ten; More or Less?
- LESSON 14: Building mental math ability
- LESSON 15: 10 more or less on a 120 chart
- LESSON 16: Continuing to build mental math skills