# Lesson 17

Calculating Products of Decimals

### Lesson Narrative

In this culminating lesson on multiplication, students continue to use the structure of base-ten numbers to make sense of calculations (MP7) and consolidate their understanding of the themes from the previous lesson. They see that multiplication of decimals can be accomplished by:

- thinking of the decimals as products of whole numbers and fractions;
- writing the non-zero digits of the factors as whole numbers, multiplying them, and moving the decimal point in the product;
- representing the multiplication with an area diagram and finding partial products; and
- using a multiplication algorithm, the steps of which can be explained with the reasonings above.

### Learning Goals

Teacher Facing

- Interpret a description (in written language) of a real-world situation involving multiplication of decimals, and write a multiplication problem to represent it.
- Use an algorithm to calculate the product of two decimals, and explain (orally) the solution method.
- Use an area diagram to represent and justify (orally and in writing) how to find the product of two decimals.

### Student Facing

Let’s multiply decimals.

### Required Preparation

Some students might find it helpful to use graph paper to help them align the digits for vertical calculations. Consider having graph paper accessible for the activity: Calculating Products of Decimals.

### Learning Targets

### Student Facing

- I can use area diagrams and partial products to represent and find products of decimals.
- I know how to use a product of whole numbers to find a product of decimals.

### Print Formatted Materials

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Student Task Statements | docx | |

Cumulative Practice Problem Set | docx | |

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Teacher Presentation Materials | docx |