SWBAT solve missing part story problems using their understanding of base 10.

Go round and round...Round and round...round and round! Sing The Wheels on the Bus while students apply base 10 understanding to change problems.

10 minutes

**CCSS Context:**

In first grade, students are expect to add and subtract within 100 (1.NBT.C4, 1.NBT.C6). This lesson is very much an extension of these standards. Students apply their understanding of different kinds of word problems, as well as their understanding of place value, to solve these problems. This lesson can be used as an extension in first grade, or as a lesson to align with 2.OA.1 in 2nd grade!

**Read Aloud & Hook:**

I'll read aloud Pete the Cat: The Wheels on the Bus. After I read it, I'll show the video version available on youtube here!

**Objective:**

How can I use what I know about 10 to help me solve for the missing part?

17 minutes

**Present Problem: **There are 64 people on the bus. When the bus stops, a group of friends get off the bus. Now there are 35 people on the bus. How many people got off the bus?

ï»¿Focus Questions:

- Retell the story problem.
*This helps students practice MP1, Make sense of the problem, and will help them identify what part of the problem is unknown.* - Did the number of people on the bus increase or decrease? How do you know?
- Partner Plan: How will you solve this problem at your desk?

**Student Work Time: 8-10 minutes**

As students work, I am circulating, looking for student strategies to share. You can see one student's strategy here: Student Work Example. It shows how this student used base 10, then broke the ten. Most students will directly model, which means they will act out the problem using a concrete model, if this is one of their first times seeing a problem like this. The student work example shows how students can represent their thinking in a picture!

15 minutes

I'll choose 2-3 students to share their strategies with the class. I am anticipating that most students will directly model this problem, meaning they will take out the 64, and take away until they get to 35. However, I also want to see if students start with 64 and just take away 35. This would show that they have an understanding of a property of subtraction that I would want to explore as a class.

If this happens, I'll ask the following questions to students:

- What's the same about the 2 strategies?
- What's different about the 2 strategies?
- What's different about the number sentences that match these strategies?
- Where is the answer to the story in each equation?

After strategy share, I'll have students partner talk about how the strategies were the same and different.

15 minutes

Students solve problems on their own using the packet: Bus Base 10 Independent Practice. They are either applying strategies they heard from the debrief or practicing a strategy they already used today. However, during this time I'll differentiate the number set based on what I saw in the student share problem.

**Group A: Intervention**

I'll have these students work with numbers under 50, on the decade. These students probably struggled when they were solving earlier, particularly getting stuck on trying to handle the number set.

**Group B: Right on Track**

Students will get numbers under 75. Students may have to compose/decompose a ten like they had to in the student share. For the missing addend problem, I'll use 54 + ____ = 70. For the missing subtrahend, I'll use 63 - ___ = 39

**Group C: Extension**

Students get numbers under 100. Students have to compose/decompose a ten like they had to in the student share. Examples: 76 + ____ = 100; 93 - ___ = 64

20 minutes

Students complete the Base 10 Assessment to show their understanding of base 10. It includes problems to assess how they solve 10 more and 10 less problems, as well as a story problem where they show how they subtract within 100.

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