The purpose of this activity is for students to use their understanding of place value to find the number that makes each equation true. Students must consider how units may be composed or decomposed to find the unknown number (MP7). The number choices intentionally emphasize the types of compositions and decompositions students may use to add and subtract within 1,000. The Synthesis focuses on the equations that involve composing or decomposing two units.

• “How do you pick a number to make this equation true?”
• “Can you show me how to use base-ten blocks to represent the side of the equation that tells how many of each unit? How can you compose or decompose units to show the equation is true?”

• Invite previously identified students to share their method for finding the unknown number for 2 hundreds + 9 tens + 17 ones = _____ hundreds + 7 ones.
• For students who use base-ten blocks, draw place value diagrams to record their explanation.
• Consider asking:
  • “How do you know both sides of the equation are equal?”
  • “Did you compose or decompose units? Did you compose or decompose more than one time?”

The purpose of this activity is for students to use their understanding of place value to find and create matching expressions. The activity encourages students to write expressions that show the same value by composing or decomposing hundreds, tens, and ones. Although students may find the value of each expression to find matches, look for the ways they reason why two expressions match or do not match by using what they know about hundreds, tens, and ones (MP7).

• Invite 1–2 previously selected students to share a set of matching cards.
• Consider asking:
  • “Do you agree that these expressions match? Explain.”
  • “What other expressions did you write that match these expressions?”