# Lesson 17

Does It Make Sense?

### Lesson Purpose

The purpose of this lesson is for students to use mental computation and estimation strategies such as rounding to decide if answers to two-step word problems make sense.

### Lesson Narrative

Previously, students extended their understanding of addition and subtraction within 1,000 and learned how to round to the nearest ten and hundred. In this lesson, students work with two-step word problems and decide if a given answer for a two-step problem is reasonable. Students estimate answers to two-step problems and determine if each other's solutions make sense after they solve two-step word problems in a way that makes sense to them.

• Engagement
• MLR8

Activity 2: Solve and Reason

### Learning Goals

Teacher Facing

• Assess the reasonableness of answers using mental computation and estimation strategies including rounding.
• Solve two-step word problems using addition and subtraction in a way that makes sense to them.

### Student Facing

• Let’s decide if our answers make sense.

Addressing

Building Towards

### Lesson Timeline

 Warm-up 10 min Activity 1 15 min Activity 2 20 min Lesson Synthesis 10 min Cool-down 5 min

### Teacher Reflection Questions

Reflect on students’ assessment. Are they able to flexibly use different strategies, such as considering the answer in context, rounding, or estimating? How can you leverage their previous experiences with sense making and rounding to help them keep reasonableness in mind?

### Suggested Centers

• Tic Tac Round (3–5), Stage 1: Nearest Ten or Hundred (Addressing)
• Number Puzzles: Addition and Subtraction (1–4), Stage 5: Within 1,000 (Addressing)

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