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# Making the Minus Make Sense

Lesson 5 of 12

## Objective: SWBAT explain what each mathematical symbol (+ and -) mean. SWBAT represent what is happening in a story problem with a subtraction equation.

#### Setting Up the Learning

*5 min*

In first grade, students are expected to be able to solve a variety of types of addition and subtraction story problems and represent them using an equation (1.OA.1). This lesson focuses on the story problem that some students tend to struggle with a little bit more-subtraction!

**Review:**

Yesterday we discussed how mathematicians use the + and - to represent their thinking. Today we are going to zoom in on how to write equations that have a minus symbol.

**Connect: **

Using symbols helps us write all of our thinking really quickly. It helps us write using only numbers and symbols-no words!

**Objective: **How do I write a matching subtraction equation?

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#### Opening Discussion

*10 min*

I'll start this lesson by sharing out one of the subtraction problems from yesterday's lesson. (Go to this link for how I introduced the + and - symbol together).

I'll choose a direct modeling strategy-one where a student acted out the problem with cubes to share. The focus of the share is on what we did first, next and last in the problem to provide a scaffold for how we write the equation.

**Read problem: You have 15 soccer balls in your shopping cart. You give 4 soccer balls away. How many soccer balls are in your shopping cart now?**

**Guiding Questions before I share the strategy: **Visualizing problems is KEY to helping kids understand why they use the + or - symbol, and what each number means. These questions help students "make sense of the problem" (MP1) before they attempt to solve, represent their strategy and write an equation to match.

- Reread the problem to your partner.
- Close your eyes and visualize what is happening. Will you have more or less soccer balls in your shopping cart in the end?
- Are we putting together or taking away? What symbol do we use to represent that?

After I share the strategy, we will focus on how to write the equation.

**Scaffolding Questions: **These questions help set up students to think about retelling the problem, which actually will help guide them to being able to write the equation to match it!

- What did you do first? What happened next? What happened last?
- Let's write that in numbers and symbols.

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**Present new problem: There are 10 frogs in the pond. 3 of them hop away. How **

**many frogs are in the pond now?**

Guiding focus before students go and solve: Students retell the story to a partner and determine if it is “put together” or “take away”.

**Student Work Time: **

Students work for 5-6 min on solving and representing how they solved the problem in their math journals.

**Strategy Share:**

Students first share their own strategies from their math journals. **See attached video for an example of a partner share!** Having students discuss their thinking pushes them to **CCSS.Math.Practice.MP3 Construct viable arguments and critique the reasoning of others.**

After students partner share, I'll choose one strategy to share. Because students have been working on subtraction strategies for a couple of days, I'll quickly share out a more difficult strategy than just cubes, such as counting backwards or using a number line.

**Guiding Questions:**

- Did we put groups together or take away?
- What symbol do we need to use then?
- What number will I write first? What symbol? How many did I take away?

#### Resources

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#### Independent Practice

*15 min*

See this video for how I differentiated the independent practice!

See attached documents! I left the numbers out of the story problems so teachers can write in numbers that work best for theirs students.

#### Resources

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#### Closing

*5 min*

Students will end the lesson by doing a quick partner strategy share, focusing on how they wrote a matching equation.

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- UNIT 10: Solving 3 Addend Problems
- UNIT 11: Missing Parts: Unknowns in All Positions
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- UNIT 16: What the WHAT?! Teaching Challenging Story Problems

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- LESSON 2: Crayon Box Combinations
- LESSON 3: Wave a Magic Wand
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- LESSON 5: Making the Minus Make Sense
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- LESSON 7: There were 15 zombies...
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