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Three-Digit Addition with Base-Ten Models
Students will be able to use base-ten models to solve three-digit addition problems.
- Tell students that today they will use base-ten models to solve addition problems.
Explicit Instruction/Teacher modeling(10 minutes)
- Begin by displaying the ones unit block from your base-ten block set on your document camera. Ask students to volunteer what this represents.
- Do the same for the tens and hundreds pieces.
- Review the meaning of digit and explain we will be working with three-digit numbers today.
- Using the base-ten blocks, make a three-digit number (e.g. 246) on the document camera. Ask students to turn and tell a partner the number.
- Ask students, "How can we represent this number if we do not have blocks? Is there a way to draw them?"
- Show students that each hundreds block can be represented with a large square, each tens block can be drawn as a thin rectangle, and each one block can be drawn as a small square.
- Demonstrate by drawing the number 246 in three columns (labeled H, T, O), keeping the hundreds on the left, the tens in the middle, and the ones on the right.
- Introduce a second three-digit number, such as 152.
- Draw 152 directly underneath 246 so the hundreds, tens, and ones are aligned.
- Have partners turn and talk about how to add these two numbers using our drawings.
- Demonstrate adding the numbers starting with the ones place and moving left. If regrouping is needed, you can cross out and add to the column on the left.
Guided Practice(10 minutes)
- Have student helpers assist in passing out whiteboards, markers, and dry erase markers.
- Instruct students to draw the three columns labeled H, T, and O.
- Give students two or three problems to solve using base-ten drawings. Make sure at least one problem includes regrouping.
- After giving students time to solve each one, have students hold up their whiteboards so you can assess understanding.
- Assist struggling students.
- Have student helpers collect whiteboards, markers, and erasers.
Independent working time(15 minutes)
- Distribute the Triple-Digit Addition worksheet and scrap paper.
- Instruct students to write their names on both pages.
- Explain that the worksheet is where they will write their answers and the scrap paper is where they will show their work using base-ten models for each problem. Demonstrate on your own copy of scrap paper how to label their work with the corresponding number from the worksheet, so you can quickly check their work.
- Allow students to work independently on the problems as you circulate the room answering questions.
Enrichment: Provide fast finishers with bonus problems featuring regrouping on the board.
Support: Pull a small group to work on the worksheet while other students work independently.
- Circulate and support students, reinforcing the base-ten model method and checking for understanding.
- Collect the worksheets and scrap paper and assess for understanding of the value of each digit, vertical adding in each column, and regrouping ability.
Review and closing(3 minutes)
- Call students to the rug and ask for two student volunteers to share a three-digit number.
- Ask a third student volunteer to draw the base-ten models for each number and solve.
- Ask students to show you on their fingers how comfortable they feel with this strategy. If they are very comfortable with addition using base-ten drawings, they will hold up five fingers, if they are still feeling very unsure, they will hold up one finger, three fingers for gaining confidence, and so on.