Number Sentences

Solve to Find Unknowns. Give students a few open number sentences with more than one addend on each side of the equal sign. Have some sentences reflect base-ten partitions of a number and the others reflect other partitions. For example:

1. 20 + 17 = n + 7
2. 36 + 8 = n + 9
3. (5 × 100) + (4 × 10) + 3 = 500 + n + 3
4. 300 + n + 12 = 200 + 120 + 2
5. 112 + 32 = 110 + n

Have students work in pairs to solve the problems and determine the unknowns. As discussed previously, do not direct students to strategies or a series of formal steps. When students finish, ask volunteers to explain their strategies and show their solution paths on the board. Encourage other students to ask questions or make comments. After one student has explained his or her strategy, ask another student to explain the strategy in his or her own words. Ask students to solve additional problems using a particular student's strategy. See the Sample Dialog.

After the discussion, ask students to solve the following problem individually.

100 + 70 + n = 200 + 80 + 5

Show What I Think. Have students explain their thinking as Tanya and Romesh did in the Student Guide pages. Students write their explanations in the speech bubble on the What I Think Master and draw and color their own faces and hair on the silhouette. Remind them of Math Practices Expectation 5 on the Math Practices page in the Student Guide Reference section:

MPE5.

Show my work. I show or tell how I arrived at my answer so someone else can understand my thinking.

Have students work individually to solve the problem and fill in the thought bubble. Have partners read one another's “thoughts” and ask questions until both partners understand both explanations. Ask them to revise their explanations based on their partners' questions. As students work, ask two or three students to share their solutions on displays with the class. Choose different representations such as words, number sentences, or number lines. Have students ask questions of the presenters to clarify the explanations.

Select Practice for Number Lines and Number Sentences. Distribute the feedback you prepared for each student on Check-In: Questions 11–14. Refer students to the Practice Menu on the Number Lines and Number Sentences page in their Student Activity Book. Have students think about the questions in the left-hand column of the menu. Ask students to review their work on Check-In: Questions 11–14, your feedback, and other work from Lessons 1 and 2 to decide which problems to choose from the following groups:

1. Students who are “working on it” and need some extra help should circle the problem set marked with a triangle (). These problems provide scaffolded support for developing the essential underlying concepts as well as some opportunities for practice.
2. Students who are “getting it” and just need more practice should circle the problem set marked with a circle (). These problems mainly provide opportunities to practice with some concept reinforcement and some opportunities for extension.
3. Students who have “got it” and are ready for a challenge or extension should circle problems marked with a square (). These problems provide some practice and then move into opportunities for extension.

Check students' choices to see how well they match your own assessment of their progress on the related Expectation(s). Help students make selections that will provide the kinds of practice they need.

Ask students to complete the appropriate problems as homework. Remind students to adjust their choices from the menu if problems seem too easy or too difficult.