Subtraction

Ask students to discuss the problems in Question 11 of the Subtraction pages in the Student Guide. Do not ask them to solve the problems yet, but instead to talk with a partner about how they would solve them.

Make a table on the board or overhead with columns labeled “Paper-and-Pencil Method” and “Mental Math Strategies,” like the one in Figure 16. Consider adding a third column labeled “Both” in case students disagree about placement of a problem.

Have students decide the column in which they would place each problem in Question 11.

Question 12 asks students to choose problems from Question 11 and prepare to tell how they would solve them mentally. Give them time to talk with a partner about their ideas and then ask them to take turns describing their solutions to the class so the class can add the strategies to the list they made at the start of the lesson.

Encourage them to make connections with strategies previously discussed and to give a name to their strategies.

After students have discussed their own mental math strategies, ask them to look at the strategies described in the Student Guide by students in Mrs. Dewey's class. These are of two basic types: counting back and counting up. Ask students to examine the solutions presented in the book and then compare them to strategies the class listed in Questions 11 and 12 and at the beginning of the lesson.

Ask students to solve the problems in Question 13 using some of the methods of the students in Mrs. Dewey's class. Then ask volunteers to share their solutions with the class.