Lesson 15

The purpose of this Number Talk is to elicit strategies and understandings students have for dividing by 8. These understandings help students develop fluency and will be helpful later in this lesson when students will need to be able to divide when solving problems.

When students use multiplication facts they know to divide and then add or remove groups of 8 for facts they are less familiar with, they look for and make use of structure (MP7).

• Display one expression.
• “Give me a signal when you have an answer and can explain how you got it.”
• 1 minute: quiet think time

• Record answers and strategy.
• Keep expressions and work displayed.
• Repeat with each expression.

• “How did knowing \(80 \div 8\) help you find the other values?”
• Consider asking:
  • “Who can restate _____’s reasoning in a different way?”
  • “Did anyone have the same strategy but would explain it differently?”
  • “Did anyone approach the problem in a different way?”
  • “Does anyone want to add on to _____’s strategy?”

The purpose of this activity is for students to put together their knowledge of problem solving, measurement topics (time, weight, and liquid volume), and equal groups to solve a variety of problems about a day at the fair. After solving problems, students create a poster about the day.

Students should feel free to display their work in creative ways while making sure that the mathematical thinking on each problem is made clear. If they want, students could create individual posters rather than working with a partner.

Throughout the activity, students reason abstractly and quantitatively as they interpret the different problems and situations, represent them, and find solutions (MP2).

• Groups of 2
• “We’re going to solve some problems about a day at the fair. What are some things you could do during a day at the fair?” (go on rides, walk around, eat fair food, look at some of the animals)
• 30 seconds: quiet think time
• Share responses.
• Give each group tools for creating a visual display.

• “Work with your partner to solve four problems about a day at the fair. You’ll get to choose some of the activities at the fair.”
• “Then, create a poster that shows your mathematical reasoning and solutions for each problem.” 
• “Feel free to be creative in how you put your ideas on your poster, but make sure to organize them so that they are easy for others to understand.”
• 25 minutes: partner work time

• Display the student posters around the room.

The purpose of this activity is for students to consider strategies different from their own (MP3) and aspects of student work that make mathematical ideas clear as they visit the posters created in the previous activity.

• Display posters from the previous activity.

• Groups of 2

• Have half the students stand at their poster with their partner to share their ideas or answer questions as the other students visit their posters.
• Have the other half of the class visit their classmates’ posters with their partner.
• 5 minutes: partner work time
• Switch student roles and repeat.

• “Today we created posters that put together a lot of the problem solving skills we have been learning all year.”