Lesson 15

Multiplying Rational Numbers

Lesson Narrative

The purpose of this lesson is to provide students with practice multiplying rational numbers. Students see products of three numbers, and figure out what to do with a product of three negative numbers by grouping two of them together and multiplying those first. They see products involving unit fractions, reminding them that dividing by a whole number is the same as multiplying by its reciprocal. This will be useful in the next lesson when they start to divide rational numbers. There is an optional activity where students can use another approach to understanding why the product of two negative numbers is positive, by examining patterns in an extended multiplication table that includes both positive and negative numbers (MP7).

Learning Goals

Teacher Facing

• Identify multiplication expressions that are equal, and justify (orally) that they are equal.
• Multiply rational numbers, including multiplication expressions with three factors, and explain (orally and in writing) the reasoning.

Student Facing

Let’s get more practice multiplying signed numbers.

Required Preparation

For the Card Sort: Matching Expressions activity, prepare 1 copy of the blackline master for each group of 2 students. If possible, copy each complete set on a different color of paper, so that a stray card can quickly be put back.

It is optional to provide 1 copy of the Rational Numbers Multiplication Grid blackline master to each student.

Student Facing

• I can solve problems that involve multiplying rational numbers.

Building On