# Lesson 15

Find Missing Side Lengths

### Lesson Purpose

The purpose of this lesson is for students to find missing side lengths of rectangles and rectangular prisms using their understanding of area, volume, and multi-digit division.

### Lesson Narrative

In an earlier unit, students learned to find the volume of rectangular prisms either by multiplying the length, width, and height or choosing a base and multiplying the area of that base by the corresponding height. In this unit, students learned to use division strategies to divide multi-digit numbers. The purpose of this lesson is to use multiplication and division to solve problems about area and volume. Throughout, students apply multiplication and division and what they know about the relationship between the length, width, and height of a rectangular prism and its volume to solve problems (MP2).

- Engagement

- MLR8

### Learning Goals

Teacher Facing

- Solve problems involving area and volume using the relationship between multiplication and division.

### Student Facing

- Let’s use the relationship between multiplication and division to solve problems.

### Required Preparation

### 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

As you finish up this unit, reflect on the norms and activities that have supported each student in learning math. List ways you have seen each student grow as a young mathematician throughout this work. List ways you have seen yourself grow as a teacher. What will you continue to do and what will you improve on in the next unit?

### Suggested Centers

- Number Puzzles: Multiplication and Division (4–5), Stage 2: Multi-digit Factors (Addressing)