Three-Digit Addition Strategies Review
Students will be able to solve three-digit addition problems using various visual and written strategies.
- Ask students to think about which strategies they have used to solve addition problems. Call on a few volunteers to share out.
- Tell students that today they will review strategies to solve three-digit addition problems.
Explicit Instruction/Teacher modeling(10 minutes)
- Begin by displaying a number made with the base-ten block set on your document camera. Ask students to volunteer which number this represents.
- Remind students that each hundreds block can be represented with a large square, each ten block can be drawn as a thin rectangle, and each one block can be drawn as a small square. Say, "Remember that you do not need to draw every unit within the tens and hundred! A large square and thin rectangle will work."
- Project the problem 742 + 239On the document camera. Demonstrate adding with the base-ten method by drawing the number 742 in three columns labeled H, T, and O, keeping the hundreds on the left, the tens in the middle, and the ones on the right. Directly underneath, draw 239 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.
- Next, project the problem 809 + 135On the document camera.
- Have partners turn and talk about how to add these two numbers using the number line. Then ask students to discuss how they can break up 135 into easier chunks. Ask for volunteers. Explain that one of the easiest ways to break up a three-digit number is by hundreds, tens, and ones, so today we will break up 135 into 100 + 30 + 5To make our "hops" along the number line.
- Demonstrate "hopping" starting at 809 on the left side of a number line drawn on the board or projector. Draw a half-circle hop from 809 to 909 by adding one hundred. Label the 100 on top of the half-circle hop to keep track of your chunks. Then add 30 to hop to 939. Finally, make a last hop of 5 to make it to 944.
- Finally, project the problem 457 + 161On the document camera and demonstrate adding with the standard algorithm.
- Have partners turn and talk about how to add these two numbers using the algorithm. Remind students to keep the ones, tens, and hundreds aligned, and to always start by adding the ones and moving left.
Guided practise(10 minutes)
- Have student helpers assist in passing out whiteboards, erasers, and dry erase markers.
- Instruct students to draw the three columns labeled H, T, and O on their whiteboards.
- Give students two problems to solve using base-ten drawings. Make sure at least one problem includes regrouping.
- Give students two problems to solve using number lines and two problems using the standard algorithm. Make sure at least one of each 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 Addition Within 1000 Check-in 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 and number lines 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.
- Pull a small group to work on the worksheet while other students work independently.
- Provide fast finishers with bonus problems featuring regrouping on the board.
- Provide an extra practise worksheet, such as the Triple Digit Addition practise worksheet.
- 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 each share a three-digit number.
- Ask a third student volunteer to solve and explain their work as they go.
- Ask students to show you on their fingers how comfortable they feel with the base-ten strategy. Have them hold up five fingers if they are very comfortable with addition using base-ten drawings, three fingers for gaining confidence, one finger if they are still feeling very unsure, and so on.
- Repeat the five finger check-in for the standard algorithm and number line strategies.