# Lesson 21

Classroom Supplies (optional)

### Lesson Purpose

### Lesson Narrative

This lesson is optional because it does not address any new mathematical content standards. It does provide students with an opportunity to apply precursor skills of mathematical modeling.

In this lesson, students put together a wish list of supplies they would like to get for their classroom given a large collection of choices and their costs. They are given a budget and freedom to decide how to spend the money. As they make choices, students round the costs before they check the total amount they are spending. Students then compare their wish list with a partner group. Groups compare their wish lists and how much they spent in each category.

When students make decisions and choices, adhere to mathematical constraints, interpret a mathematical answer in context, organize data, make revisions, and report results, they model with mathematics (MP4).

- Representation

- MLR8

### Learning Goals

Teacher Facing

- Add and subtract within 1,000 to solve real-world problems.
- Round whole numbers to the nearest ten or hundred to solve problems.

### Student Facing

- Let’s make a wish list for class supplies.

### Required Preparation

### Lesson Timeline

Warm-up | 10 min |

Activity 1 | 25 min |

Activity 2 | 15 min |

Lesson Synthesis | 10 min |

### Teacher Reflection Questions

### 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)
- Five in a Row: Multiplication (3–5), Stage 2: Factors 1–9 (Supporting)