This lesson is optional because it provides opportunities for additional practice with multiplying rational numbers. The main activity uses the Information Gap routine. To obtain all the necessary information, students need to persevere in asking questions (MP1) and communicate precisely (MP6).

There are two other optional activities in this lesson. In the first, students sort multiplication expressions and match the expressions that have the same value. In the second, they calculate the product of expressions and compare answers with their partner.

Some of the expressions involve fractions or decimals. Multiplying by a unit fraction serves as a bridge to the next lesson in which students will divide rational numbers. Also, some of the expressions have three different factors, so students can apply the associative property. Regardless of which two factors students choose to multiply first, multiplying that product by the remaining factor will result in the same answer.