Workshop: Multidigit Addition and Subtraction

Est. Class Sessions: 2–3

Developing the Lesson

Part 2: Multidigit Subtraction Strategies

Introduce Subtraction Practice Menu. Display and direct students' attention to the Multidigit Subtraction Practice Menu in the Student Activity Book. See Figure 4. Students will do one activity from each column of the menu. Briefly introduce the activities in each column.

Introduce and Play Path to Glory Game: Subtraction. Path to Glory Game: Subtraction is listed in the first column of the menu. Everyone will play this mental math game. Students were introduced to the Path to Glory Game in Unit 7. In this version of the game, players will start with 1000 and subtract 10, 20, 30, 100, 200, or 300 until a player reaches 0. Display the Path to Glory Game: Subtraction page in the Student Activity Book and explain the new directions to the class. Use the example on the page to demonstrate how to play.

Organize players into pairs to play the game. Game boards for several games are provided. Some student pairs may play more than one game in the time allotted. Extra game boards can go home so that students may play the game with a family member for homework.

Choose Multidigit Subtraction Practice. Display the following two problems and ask students to first estimate the differences for each one:

372 831
− 253− 568

Direct students' attention back to the Multidigit Subtraction Practice Menu. These problems are listed in the second column on the menu. Ask students to solve them any way they choose. See Figures 5 and 6 for possible solution strategies. Students may refer to the Subtraction Strategies Menu for Larger Numbers in the Student Activity Book Reference section. Have base-ten pieces available.

After they have completed the problems, ask questions such as the following:

Compare your estimate to your answer. Does your difference seem reasonable?
Who used a mental math strategy? For which problem?
Did anyone use a number line? Base-ten pieces or shorthand? Show us how.
Who used a paper-and-pencil strategy? For which problem?
Who used expanded form? Compact method? Show us how.

Modify Path to Glory. Challenge some student pairs by modifying the numbers they can subtract in the Path to Glory Game: Subtraction. For example, change some of the numbers to 25, 75, and 150.

The problems in Part 1 of the Multidigit Subtraction Practice pages in the Student Activity Book provide problems with 0–1 trades, such as 372 − 253 and a little more scaffolding. Those in Part 2 provide problems similar to 831 − 568 with 1–2 trades and involve larger numbers.

Ask the following questions to help students choose their practice:

How confident are you in your answers?
Did you need any tools to help you?
Did you solve both problems easily?
Which set of problems do you think you should choose for practice?

Tell students to circle one activity, Multidigit Subtraction Practice Part 1 or Part 2, from the second column of the Multidigit Subtraction Practice Menu.

Students use the Multidigit Subtraction Practice Menu to self-assess their abilities to subtract multidigit numbers using mental math strategies [E6] and paper-and-pencil methods (e.g., expanded form, compact) [E7].

Review Game 2 of Difference War. The third column on the Multidigit Subtraction Practice Menu lists the Difference War game. Students played one of two versions of Difference War in Unit 9. In this Workshop, everyone will play the Game 2 version of Difference War and solve 3-digit minus 3-digit subtraction problems. Display the Difference War pages from the Student Activity Book and review the directions. Demonstrate a round of the game using the display deck of digit cards you prepared prior to the lesson and a display of the Difference War Game Board 2.

Practice Multidigit Subtraction and Play Difference War When students are ready with their tasks, ask them to begin working. Remind students that they can refer to the Subtraction Strategies Menu for Larger Numbers in the Student Activity Book Reference section as they work on the problems and play the game. Have base-ten pieces readily available. As students complete the problems on the Multidigit Subtraction Practice pages, they can find a partner and play the Difference Game. Alternatively, you may decide to have the entire class move on to the game when most students have completed the Multidigit Subtraction Practice pages.

Unfinished problems in either Part 1 or Part 2 of the Multidigit Subtraction Practice pages in the Student Activity Book may be assigned as homework.

Allow students who are struggling with multidigit subtraction to play the Game 1 version of Difference War that can be found in Lesson 8 of Unit 9. This game involves 2-digit minus 2-digit subtraction problems.

Adventure Book: