# Lesson 20

Productos cuyos resultados son centésimas

### Lesson Purpose

### Lesson Narrative

The purpose of this lesson is for students to find products of two decimal numbers where each decimal represents a number of tenths, using the place value reasoning and diagrams that were also useful for finding the product of a whole number and a decimal. Students explain why \(0.1 \times 0.1 = 0.01\) in the warm-up and this opens up one strategy for finding products like \(1.5 \times 0.7\). In particular, this can be rewritten as

\(\ (15 \times 0.1) \times (7 \times 0.1) = (15 \times 7) \times (0.1 \times 0.1)\).

So the value of \(1.5 \times 0.7\) is 105 hundredths or 1.05. A second approach uses area diagrams which students are familiar with from earlier lessons in this unit and from when they used them to find products of fractions. Decimals are an example of fractions and these diagrams are useful in this situation as well.

- Representation

- MLR8

Activity 1: Productos de décimas

### Learning Goals

Teacher Facing

- Use diagrams and place value reasoning to interpret and evaluate products of two decimal numbers.

### Student Facing

- Multipliquemos décimas por décimas.

### Required Materials

Materials to Copy

- Small Grids

### 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

### Suggested Centers

- Target Numbers (1–5), Stage 8: Add Tenths or Hundredths (Addressing)
- Target Numbers (1–5), Stage 9: Subtract Tenths or Hundredths (Addressing)

### Print Formatted Materials

Teachers with a valid work email address can click here to register or sign in for free access to Cool Down, Teacher Guide, and PowerPoint materials.

Student Task Statements | docx | |

Lesson Cover Page | docx | |

Cool Down | Log In | |

Teacher Guide | Log In | |

Teacher Presentation Materials | docx | |

Blackline Masters | zip |