The purpose of this activity is to add and subtract three-digit numbers and multiples of 10 or 100, using base-ten blocks and equations. The structure of the base-ten blocks encourages students to notice that hundreds are added to or subtracted from hundreds and tens are added to or subtracted from tens (MP7). To help students focus on this structure, the numbers are chosen so that the addition and subtraction of tens can take place without composing or decomposing a hundred. 

If you do not have enough hundred blocks for each group of 2 students, organize students into larger groups.

• Invite previously identified students to share equations or display:
• Display a base-ten diagram, or, if possible, allow students to demonstrate with base-ten blocks.
• “How does the equation connect to the diagram or blocks?” (Take away 4 hundreds from the blocks and 4 hundreds and 5 ones are left over.)
• “What did you notice about how the value of the blocks changed?” (There are fewer blocks. The hundreds place changed because hundreds were subtracted.)

The purpose of this activity is for students to add and subtract multiples of 10 and 100 within 1,000. Students interpret situations, with base-ten blocks and base-ten diagrams, and use equations to represent sums and differences. In the Activity Synthesis, students relate the situation, base-ten diagram, and equation. They notice, through repeated reasoning, that when adding and subtracting, they can add or subtract hundreds and hundreds, and tens and tens (MP7, MP8).

If students draw diagrams that do not match the situation or write equations that are not true, consider asking:

• “Can you explain what you did?”
• “Do you notice any patterns when you add or subtract hundreds and hundreds? Tens and tens?”

• Invite a student to share their representation and equation for Jada’s blocks. If no students use a base-ten diagram, select a student to share how they use base-ten blocks, and use a base-ten diagram to record their steps.
• “How does the base-ten diagram show Jada’s blocks?” (The blocks show how many Jada had at the start. The lines show the 3 hundreds that were taken away.)
• Display
• “How does the equation show Jada’s blocks?” (482 is what Jada started with and 300 is the 3 hundreds she gave away. 182 is how much she has left.)