Lesson 7

This lesson allows students to solve problems that involve multiplicative comparisons in the context of cost of living. Students are presented with different cost information and asked to make comparisons in different ways. For instance, they may be given the cost in one country and told that the cost in a second country is “9 times as much”, and asked to find the dollar cost in the second country. They may be given the costs in two countries and then asked to compare the costs using a comparison statement that uses multiplication. Students also reason about how many of an item could be purchased in a country given a certain dollar amount (for example, how many months of rent in Ghana can one afford with \$2,000?).

The work requires students to use several operations and to consider estimates where the operations would go beyond grade level (MP1, MP2). In many questions, it is not important that students find exact products, quotients, or answers. The emphasis is on reasoning flexibly about relative sizes of quantities and solving problems multiplicatively.

If students need additional support with the concepts in this lesson, refer back to Unit 5, Sections A and C in the curriculum materials.

Activity 1: The Most and Least Expensive