Lesson 14

This Number Talk encourages students to think about place value and to rely on the properties of operations to make it easier to find the value of an expression mentally (MP7). The methods elicited here will be helpful later in the lesson when students make sense of and solve Put Together/Take Apart, Result Unknown problems with multiple two-digit addends.

• Display one problem.
• “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 you choose which numbers to add first?” (I looked for ways to make a ten. I looked for ways to use sums I’ve done before. I added tens first then I tried to make tens with the ones.)

The purpose of this activity is for students to represent and solve a two-step story problem. The story problem is presented in parts, and students are encouraged to represent each part in a way that makes sense to them. In the synthesis, students compare different ways they represent and solve the problem (MP2).

• Groups of 2 
• Give students access to connecting cubes and base-ten blocks.

• “Read each problem with your partner and solve it on your own. Show your thinking using diagrams, equations, or words.”
• 5 minutes: independent work time
• 5 minutes: partner discussion
• Monitor for students who use tape diagrams and equations to represent each problem.

• Invite previously identified students to share their tape diagram and equation for each part.
• “How did _____ represent the problem? How does each representation show the story problem?”
• Display \(25 + 17 + 35 = {?}\)
• “How does this equation represent Andre’s seeds?” (It shows all the seeds he has in one equation.)
• “What are other ways we could add to find the sum?” (We could add 25 and 35 first. Then add 17. We could add 17 and 35 and then add 25.)

The purpose of this activity is for students to represent and solve one- and two-step story problems using methods that make the most sense to them. Students each select a problem to solve on their own and share their work with their group. Each group uses the solutions to solve a two-step Put Together, Result Unknown problem. Students have multiple opportunities to describe and compare the different ways their peers represent and solve story problems (MP2, MP3, MP6).   

This activity uses MLR7 Compare and Connect. Advances: representing, conversing.

• Groups of 3
• Give students access to base-ten blocks.

• “Read the problems together. Each person in your group must solve one problem on their own. Decide together who will solve each problem. Be ready to share your thinking with your group.”
• “After everyone shares and you agree on how many seeds each character has, complete the story and solve the problem together.”
• 4 minutes: independent work time
• 5 minutes: small-group discussion

MLR7 Compare and Connect

• Give each group a piece of chart paper and markers.
• “Create a visual display that shows your thinking about the story problem you solved as a group.  You may want to include details such as drawings, diagrams, equations, and labels to help others understand your thinking.”
• 5–7 minutes: gallery walk
• “What is the same and what is different between the different ways we made sense of and solved the story problem?” (Some groups used more than one tape diagram and equation to represent the problem. Some groups used one equation. We added the characters seeds in different ways. We used different ways to show how we added.)
• 30 seconds quiet think time
• 1 minute: partner discussion