Lesson 5

The purpose of this True or False is to elicit strategies and understandings students have for place value and the operations of addition and subtraction (MP7). Students may use these understandings to reason about whether each equation is true or false without finding the value of the expressions.

• Display one statement.
• “Give me a signal when you know whether the statement is true and can explain how you know.”
• 1 minute: quiet think time

• Share and record answers and strategies.
• Repeat with each statement.

• “How can you explain your answer without finding the value of the expression?”

The purpose of this activity is for students to make sense of and solve Put Together/Take Apart, Addend Unknown story problems (MP2). In the synthesis, students discuss different methods used to solve these problems, including using addition and subtraction.

The teacher may want to incorporate movement into this activity by writing each problem on a piece of chart paper and placing each one in a different location around the classroom. Students can solve the problem at one location, discuss the problem with their partner, then move on to a new problem at a new location.

• Groups of 2
• Give each group access to connecting cubes in towers of 10 and singles. 
• Display the image in the student book.
• “What do you notice in this picture? What do you wonder?” (There are bright colors. This looks like stars in the sky. Why is there red in the sky? Where is this?)
• “This is a picture of something called the Helix Nebula. It is one of many interesting things that can be seen in our sky. People who are interested in learning more about stars, planets, or anything else that is found in the sky, can visit a planetarium to learn all about these things. We are going to solve some problems about a field trip to the planetarium.”

• 8 minutes: independent work time
• 4 minutes: partner discussion
• Monitor for students who solve the problem about bright and dim stars with addition and for students who solve the same problem with subtraction.

If students attempt to solve each problem by adding the known quantities, consider asking:

• “What is the story problem about? What do you know? What do you need to figure out?”
• “What did you do to solve the problem?”
• “What does your answer mean in the story? Does it make sense?”

• Display \(15 - 6 = \boxed{\phantom{3}}\) and \(6 + \boxed{\phantom{3}} = 15\)
• “How do both of these equations help you find the number of shooting stars Tyler saw?”
• Invite previously identified students to share. As needed, ask students to connect the numbers they use to the story problem.
• “How are these methods the same? How are they different?” (They both find the same number of dim stars. Both show that there’s some bright stars, some dim stars, and a total number. One way uses addition to count on from the number of bright stars. One uses subtraction to take away the number of bright stars from the total.)

The purpose of this activity is for students to identify different equations that can be used to represent the same problem. Students explain why each equation does or does not represent the story. This helps students understand that Put Together/Take Apart story problems can be represented and solved with either addition or subtraction when an addend is unknown (MP2).

• Groups of 2
• Give each group access to connecting cubes in towers of 10 and singles.

• Read the task statement.
• 10 minutes: partner work time

• For each problem:
  • Invite students to share how each equation they chose represents the problem. 
  • Invite students to share why one of the equations does not represent the problem.